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MG MGB Technical - Electric issues

So I was advised to start a new thread regarding the electrical issues iam having with the car as previously mentioned I have some things working and a few not the headlight I know has an issue with one of the wires when Mike was over he had a check found the fault could be either bad connection or possibly broken wire need to take off the tape covering wires and find out.the other problems I thought could be down to bad connections bad earth as apart from fuel gauge and one headlight everything else was working on car and now we have certain things not working .

WORKING
both indicators
Drivers side lights
Rear lights all of them
Rear screen heater
Radio/cassette
Front heater/blower
Park or side lights front and back
Speedo
Oil pressure gauge
Temperature gauge
And when last driving car overdrive was also working fine
NOT WORKING

passenger side headlight
Horn
Interior map light
Cigarette lighter
Window wipers
Fuel gauge
Tachometer

So any suggestions on how to best tackle the issues and solve the problems let me know
Thanks for looking regards Paul
PW Creswell

Paul,
you need to put that your car is a UK 1971 BGT as you don't have a 'Vehicle profile' on view for some to check.

I'll start the ball rolling, to check connections and items a kit of a long twin wire to go from battery to the furthest electric items on the car with various connector links, or test probe or multi-meter or any combination of the three.

Check connections and sections of wiring before stripping back tape coverings.

The tachometer and fuel gauge may share connections at a double bullet connector and at the voltage stabiliser, so that may be relevant.

Cigarette lighter and map light might be related - but do the interior and boot light work or not, and the horns might be related to this.

Windscreen wipers might be motor, switch or their connections or other wire connections or wires.

For the headlight not working is that on dip, high, flash or all?

And as PaulH has asked, what about brake lights and reversing lights and dashlights?

A good clear (horizontal) photo of the voltage stabiliser in situ (behind the dash IIRC) might be useful as would a photo of your fusebox with the cover off.
Nigel Atkins

Horn, courtesy light and cigarette lighter all come off the purple circuit which is the bottom fuse so that is a good bet as to the cause.

As a 1971 model the wipers and heater fan have their own fuse powered from the accessories position of the ignition switch. But if the heater fan is working the wipers not working isn't down to a fuse, you would need to check for 12v on the green/pink at the manual switch.

With all fused ignition circuits listed as working the tach and fuel gauge are not a fuse problem as such. The 12v supply to the tach is daisy-chained off the instrument voltage regulator, so with neither of those working that particular feed could have failed. It comes from a 4-way bullet connector behind the dash - four green wires, which also feeds the indicators and the HRW, so with those two working the supply to that bullet connector is good. It won't be a single earth fault as the tach and fuel gauge use different earths. Checking for 12v on either of the spades on the back of the fuel gauge and reporting back will isolate it further

What about the reversing lights and brake lights which also come off the green circuit?

Also what about the instrument lights? as they can have an affect on the tach.

The headlight is obviously a problem specific to that corner.

You will just have to work through things one by one as there are multiple problems, so no magic bullet i.e. no common point.

The simplifies Autowire drawings haven't been mentioned, the UK 1971 model is here http://www.mgb-stuff.org.uk/images/mgb6.jpg If the cursor over the drawing shows a + symbol then clicking should expand it.

The drawback with Autowire is that other than showing which components use an earth it doesn't give how they are shared and interconnect.
paulh4

I used to put up a hyperlink to download those Autowire diagrams but then I wasn't sure about their accuracy because of Haynes errors with midget drawings. I think they're good to use in conjunction with the relevant diagram in the Driver's Handbook because they're in colour so easier to follow and that the colour also makes the bullet connectors stand out more.

I've scanned the diagram from my Driver's Handbook so that I can zoom in on it on a computer screen as my eyes aren't good enough for the paper printed size to see that well.

A couple of car Midgets I've seen with previously installed PO alarms have changes to factory wiring and changes of things like non-standard parts that deviate from factory wiring and convention. which is why I suggested those photos (or did we cover the fusebox before with the wipers, I forget).

Nigel Atkins

Autowire later models are from Haynes so contain the same errors and omissions. Haynes combines more than one 'late' model into a single diagram whereas the WSM has separate 77 and 78/79 drawings, but even then there are still some changes that aren't included. The WSM isn't immune from errors either, for example rubber bumper UK cars are shown as having parking lights and indicators in the same light cluster, but that stopped with CB. However North American spec DID continue that way, but with a dual filament bulb behind an all-amber lens instead of two separate bulbs, although the WSM shows two bulbs for all RB production.
paulh4

Good information and at least a good starting point as far as I know all the back lights work but will recheck as I had said most things worked apart from fuel gauge and the front headlight now I do have issues with things that did work like horn dash lights did work again need to recheck those forgot to put those in the list .I know it wont be down to a single bad earth but probably a combination of bad connections and possibly exposed wires just going through the system think most of the issues are front of car but as I said need to recheck and report findings wont be able to work on car till Thursday as I'm back at work 12 hour shifts .
PW Creswell

Minor errors at the extremities aren't too bad as they can usually be seen and at least at the end of the circuit but the Midget ones had wrong circuits and wire colours so very confusing initially on a messed about car.

As the earlier cars' wiring diagrams are less complicated and congested they're not as bad once you can establish which year/MY the wiring relates to.
Nigel Atkins

PaulW,
Thursday gives you plenty of time to make sure your battery(ies) are fully changed and in good condition as chasing so many issues could involve a bit of time and battery juice.

To check for say working but poor earths at the rear (and front) lights you want to have the lights fully loaded with main beam on and then operating the brake lights and indictors (one side at a time) separately and together. For this you'll need an assistant or, but not as good, leave a camera videoing the lights while you operate the car's controls.

Checking on meters is fine for initial investigation but real world checking, and confirming is best. Particularly if you have a cheap digital meter or aren't diligent with every test you carry out with the test instrument.

Do record how things are before you start, notes, drawing and plenty of photos from all angles and do things one step at a time dealing with just one issue at a time. It may well be that sorting one issue could sort or partially sort another but don't let that distract you from completing the issue you started dealing with.

Something such as the dash lights rheostat (dimmer) I'd bypass at the start, by putting a link wire connection to take it out of equation whilst sorting the individual bulbs, connectors wires, earths. Once they're fully sorted and tested you can then reintroduce the dimmer and if all the dash lights play up you know your suspect. Also gives you the chance to (test and) clean the item's connections (internal and external). I'd also do this with other simple switches or items as somethings can play up intermittently or when combined with another item(s)/connection(s)/wiring.

Obviously the link connection needs to be well made and tested otherwise it could be introducing a or the problem.

I also like to use the long test wire direct from battery posts to items to see if and how they work with a full clean supply and compared to normal car supply (through connections, switches, etc.). This is where the selection of made up wired connectors comes in.

The test wire(s) and connections can include a test light, switch and fuse as required. Making up the test wires and connections (and testing them) gives good practice for replacing connectors and wires on the car if required.

Where possibly each time switch off or disconnect live supplies to keep stray sparks down to a minimum.

At least electrics are generally the less dirty and greasy job on the car, still often a complete PITA but at least you have a greater stock of enthusiasm than the likes of me.
Nigel Atkins

Well didnt manage to get a look at car on Thursday or yesterday basically raining. So got a break today so took some pictures of the total mess under the engine bay.cleaned up the fuse box and checked fuses while out at car other than that just looking the wires visually before I start to try and sort them out .its so bad I'm thinking of just getting a quote to maybe replace the front end wiring loom .





PW Creswell

The electrics have been working before, the cold damp weather will help to highlight week areas but I think you could work your way a through most of the issues and then when better weather is about sort what's left.

For a start all connections need to be clean, secure and protected to get the best out of them and if too many connections are weak you will have items that don't work well or at all.

There seems to be a fair bit of green crud on the fusebox holders, crud on them and the fuses with weaken flow through them. With the battery disconnected clean the fuses holders and fuses (ends) and you can then work from there.

If you've not already done so you should start from the battery with checking, cleaning, securing and protecting. The battery is new so provided the battery post clamps were also clean (on inside particularly) you can move on to checking the ends of those cables for good clean connections and move on.

It's not difficult work just a case of being methodical and working on one line at a time sorting as you go along.

The systems are quite robust and work even against not being the best and even bodgery. With the confidence gained from getting some stuff sorted you could more on to improving things.

Getting the horns working will probably help with sorting the map light and sorting the fuel gauge may help with the tacho.

You can buy part looms but any decent auto electrician would also want to sort the connections to and from the part loom which is increased labour time and cost.
Nigel Atkins

You seem to have most/just about the fusebox connections so that's a good start.



Nigel Atkins

Well having looked at fuse box it might I did clean it up after the pictures were taking did get the tachometer working if briefly if weather is ok tomorrow will have a go at cleaning up the the connectors going to the fuse box see if that makes any difference and go out from there
PW Creswell

As well as everything else being a mess as you say that fusebox is corroded and has paint on the spades which won't help. There are riveted connections on the back and they can corrode and go high-resistance as well as the spades and the fuse clips.

Did you ever tell us what was on the dial of the tach, RVI or RVC? If it's a 71 then it would originally have been an RVI, changing during 1972 and the two systems are very different. No fuse involved in the ignition, starter or tach circuits originally, but could be anything now.

With an RVI the ignition supply to the coil is routed via an inductive pickup on the tach. If the tach isn't working at all then it could be the tach or the wiring, but some wiring faults wouldn't allow the engine to run so based on the other thread that's not the case. Also because the tach works sometimes and not others that would eliminate more wiring problems with an RVI tach, leaving the 12v (green) and earth (black wire under one of the knurled nuts that hold the tach in the dash) or a fault with the tach itself as the cause.

paulh4

(ETA: I typed this before seeing PaulH's post so there might be repeats, such as rear of fusebox but this just confirms its importance.)

All connection cleaning work should be done with the battery fully disconnected.

Each connection (on/in switches and on controls and earths too) that is clean, secure and protected is better than not.

You could unscrew the fusebox and check the back of the fusebox and its connections and links are clean and the area of painted panel it's screwed to.

Note: it is very important that the fusebox is refitted the correct way up so that the link between fusebox posts 1 and 3 (see image I posted earlier) has the red/green supply wire the top two fuses for the four red wires (and not linking the green and purple wires).

You could perhaps leave all the wires connected to the fusebox whilst you remove it to check and clean it - but if you remove the wire connections from the fusebox carefully individually marked each of them and record them BEFORE doing so.

All connections need to be secure but be careful with the red and blue modern added crimp bullets going to the black covered connectors as if they're the original style traditional bullet connectors under the black cover they are a different size to the modern bullets. You don't want to force their connection if they're fine but if there's crud it will need cleaning off. Even if you can't see crud a quick spray of electrical contact cleaner is advised.

Wires also need to be secure to the connectors and protected with their insulation or connector insulation.

Once you've checked and sorted your main battery cables and earths and sorted the connections on the fusebox I'd suggest you follow the green wires and their connections, one green wire at a time.

Then purple wires, followed by red wires.

Then you could do the other side of the fuses and work back from the fusebox following the red/green, white, brown wires and their connections.

The inside contacts of switches can be cleaned (initially at least) by turning them fully on and off a dozen times or so, that simple.

Connections include bulb holders and bulbs, which also gives you the chance to clean the inside of the lights' lenses and reflectors (wipe reflectors with a damp then dry cloth only, don't use any polish, I made that mistake once). You may then notice having cleaned the all the lights' electric connections, lenses and bulbs that your lights are now brighter, good to see and be seen with.
Nigel Atkins

BTW if you choose to disconnect the battery before doing any work only ever disconnect the earth connection first, and reconnect it last. Doing it the other way round can result in some spectacular flashes and bangs, particularly with MGB batteries situated at they are.
paulh4

In my world that would be a satisfying mess to sort out.
The overspray (why/how do people do that?) would have to go, if for no other reason than to properly see the wire codes!
The "tap" connectors would have to go........hate them.
The insulated crimps would also have to go. Full insulation means you can't see if you are actually crimping on copper or insulation.
The main issues are off the bottom 2 fuses.
The bottom terminal 8 (purple) seems to be white (besides a purple) going to a bullet connector with insulated bullet males, that purple circuit feeds the horns, interior lights, headlamp flasher, cigar lighter. I can see 2 purple (I think) in that connector.............what is the other one doing? Check it out.

The next fuse up has ignition feed from the switch (white??) on the left (spade 5) through a fuse to the green circuit. This circuit is responsible for wipers, washers, tachometer, indicators, rear screen heater, brake lights, heater, reverse lights and electrical gauges (probably just fuel gauge on yours).
So you can where most of your issues are coming from.

The inoperable headlamp is more likely down to a bad bullet connector , with earth or lives just inside the inner wheel arch. Or, of course bad bulb!
As said follow the circuits and don't rely on those crimps or the tap connectors..............definitely not those.
If the spades on the fuse box feel loose, I would just replace it.

And get some thinners out and get rid of the overspray.
Allan Reeling

Allan,
I think the thicker white wire on post 8 going to the double connector might be to make up the four purple wire connections at post 8 as the thicker purple wire below it on the fuse box is a single wire (but obviously just speculation). It's not been mentioned if the hatch light and headlight flasher work or not.

As Paul wants to use this car as a daily and has limited time to work on it and I think (like me) doesn't have the luxury of a garage the whether limits when it can sensibly be worked on I think it's better to put up with the mess for now and get as much working as possible with what's already there. Then in better weather make the improvements.

I don't mind (the correct) fully insulated crimp connectors as with a bit of practice you soon learn how long to make the bare wire for good connection and leave the insulation covering.

Given there's at least one extension to a loom tail and the general mess and that all (except red/green) are single colour covered wires I think I'd add in extension wires if I had to when cutting out some of the wrong connectors or rewiring.

I think the Scotchlock has to stay for now as it's got a blue wire going to something I can't really make out (suppressor?).
Nigel Atkins

It's certainly a mess whichever way you look at it. The tape has been hacked off the main harness where it passes under the fusebox and relay which one would hope was done more to investigate a problem than to make a change.

The Scotchlok at the bottom has a white/green which is almost certainly the accessories circuit, which fed an in-line fuse under the fusebox going to a green/pink. It was this green/pink that fed the wipers and heater fan (and radio) during this period, not the green circuit.

There were separate main and rear harnesses for all years and various smaller sub-harnesses later on. I'm not aware of 'part harnesses' being available i.e. something that would need splicing into the remains of an existing harness.
paulh4

I can't see enough off the photos, or know enough, about the loom being unwrapped and I was wrong then in thinking there were more partial loom bits available but you can have whatever you want made up (at a cost of course).

Having seen a couple of wiring 'jobs' on Spridgets I'd never have any certainty with DPO wiring, but I did wonder if the blue off the white/green might be something to do with the radio/cassette, which if you remember stopped working when the wipers were being attended to previously.

One of the red wires appears to have already been extended, the butt connector along with some other crimp connectors *look* to have been done with at least a reasonable crimp tool, but then they appear to go into a traditional bullet connector.

All a bit odd but who knows what goes on with previous owners and why.

But things have been working despite the look of the wiring so hopefully they can be got going again for now without too much hassle.

Nigel Atkins

I have seen many fuse boxes that look clean but the actual connectons on the back side are questionable. I just clean them well and drop a bit of lead solder to each rivit head to ensure continuity.
You might surprise your self what that little bit of solder will do,
Sanders

Well having got the fuse box off the back was really corroded.price for a lid which I did need as I hadn't got one was £6.50 price for complete box with lid £9.50 so got a new box fitted then cleaned up all the connectors to box .horn now works but wipers headlight lighter map light fuel gauge tachometer not working so looking at some of the connectors they do look very corroded and the wire running to headlight has one wire blue/white or possibly green/white anyway one end the wire is broken so I will take a picture is still attached but not all the wire is like the separate strands are broken.was thinking of replacing this wire with new and new connectors both ends any thoughts on best way would be helpful thanks for looking regards Paul
PW Creswell

https://www.ebay.co.uk/itm/PRO-Ratchet-Crimper-Plier-Crimping-Tool-Cable-Wire-Electrical-Terminals-Kit-Set-/284191230339?_trksid=p2349624.m46890.l49286




Was thinking of buying this but not sure if it has correct bullet connectors or not
PW Creswell

Forgot to add what type of wire would it be 30amp or less for this thanks again regards Paul
PW Creswell

I thought I'd sent you details before but perhaps not.

There are two types of connectors your dealing with, the Lucar spade type that go to fusebox and switches, which can use fully insulated connectors as that kit you put up and the traditional bullets and connectors which use a different ratchet crimper and bullets.

That kit you linked to might be alright but I wouldn't buy it as cheaper connectors can be unreliable which is what you already have.

The tools, auto wire striper and ratchet crimper are what you want but again better quality tools make the work easier.

The kits with a wide range of fittings are a waste as they don't have enough of what you want and too much of what you probably wont ever use.

I'd have plenty of the connectors you need to have spares to practice with and to make up connectors for test kits and for actual use. The wire you practice on can be just short lengths of and spare cables of about the right wire gauge.

You also want a good wire cutter, the ones on those tools are too cumbersome to use in many places, a 6" or 8" CK or similar may seem expensive but if you use them properly they could last years and decades.

I normally use 2mm or 1 mm thin wall, nominal 25a and 16.5a.


Nigel Atkins

Below the traditional style bullets that go into the black sleeved traditional style bullet connectors. The traditional bullets are a different size to the insulated modern style you have on your car and in that kit you linked to. The bullets need to be sized against the thickness of the cable you are using particularly if crimping.

And ratchet tool, there are also closing tools to push the bullet(s) into the connectors.

The cost of good tools are easily offset against the cost of labour and the hassle you can get with cheap tools.







Nigel Atkins

https://www.ebay.co.uk/itm/4-7mm-Brass-Bullet-Connectors-Sockets-Lucas-Style-Wiring-Terminals-PACK-25-/193416694362?_trksid=p2349624.m46890.l49286


So this would be the type of connectors I need although the ones on car at front certainly are more like the ones in kit could explain why connectors are not sitting in the sleeves properly as well cause wrong size
PW Creswell

These two connectors are not lucas type and are different from each other


PW Creswell

As you can see the wire is broken this is the one for front headlight so need to replace this again the bullet connectors on this are not lucas ones


PW Creswell

Paul,
you're starting to pick all this up now, connectors, wires, photos and importance of all.

Don't be stingy with buying terminals as you might end up needing more than you expect plus you need some for practice wiring to make sure you're getting good practice connections and making up test wire connections with various terminals for test wires.

The link you put up is for the correct style crimp bullets and connectors, for 2mm wire

1 mm wires will need 1mm bullets and thinner wires need different sized bullets for the wire size.

As you have seen the traditional bullets are listed as 4.7mm whereas the two pre-insulated crimp modern style bullets are 4.0mm and 5.0mm so neither are a good fit to the traditional 4.7mm black sleeved connectors.

The broken blue/white wire should go to high beam so is for the biggest wattage filament of all the bulbs on the car (as standard).



Nigel Atkins

Wire/cable
Generally speaking most cables on a B are either 14 strand x 0.30mm, 8.75 amps; OR 28 stand x 0,30mm, 25 amp.
There are of course heavier cables but these 2 do most of the lighting, wipers etc.
It's easy to determine what you have, if you have access to an end and can fan the strands out.
It's also a decent indication to just measure the O/D of the insulation.
PVC wires are 2.7mm and 3.4mm respectively.
Thinwall around 1.8mm and 2.5mm.
Allan Reeling

Wipers (and heater fan) should be off an in-line fuse under the fusebox - white/green to green/pink, you showed a white/green earlier. If neither work that would be the first place to check, otherwise the manual switch.

Lighter and map light should be off he purple circuit and if the horns now work it's not that fuse.

Fuel gauge and tachometer are at the end of a chain of the green circuit that comes through a 4-way bullet connector behind the dash that also feeds the indicators and heated rear window. So again if those two work power is reaching that bullet connector, so you need to check all four wires in that are making a good connection, then check the instrument voltage stabiliser (supplies the fuel gauge), and the daisy-chained green onto the tach. Also check there is a black earth wire under one of the knurled nuts that holds it in the dash, but if that is missing the tach usually works until the lights are turned on.

But was mostly said in mid May. You need to use a voltmeter to see what is happening, wires connected and circuits turned on.
paulh4

Time for an update so got a bit if time and good weather to have a go at electrics starting from under dash good look about checking if any loose connections and checking for corrosion cleaning any with Emery paper and finishing with some of that spray used for cleaning any dirt grease etc from electrical components. Result wipers, map light,cigarette lighter ,rear screen heater all now working .front light needs the wire looked at and probably replaced tachometer again it has to be a loose connection just trying get proper access did notice at the back has two black earth wires on either side? Both look ok problem might be further back towards front of car .anyway it's getting there.
PW Creswell

There you go progress. Emery might be a bit rough but if it works, if you add something to protect the internal electrical connections stop the connections furring up again that'll stop worries about future damp weather.

Black wires are normally earths could they be for gauge lights or one for the tacho(?), they go between a round knurled nut and a gauge holding leg that earths via the metal dash front.

Depending what the blue/white wire connects to, or is supposed to be connected, and if it's long enough you might get away with just fitting a new bullet but it all looks a bit odd so possibly more will be required.


Nigel Atkins

Both wires are attached with a nut I will try and get a picture if possible
PW Creswell

Black earth wires are usually daisy-chained from gauge to gauge and are for the night-rime illumination as well as the tach electronics. As such it would be normal to have two black wires on some of the gauges, both terminated in a single through-hole terminal, on one of the two tach and speedo mounting posts. But if a PO has done any wiring there could be more.

Normally a knurled nut holding the gauges in, if it's a hex nut that's an indication someone has been in there making changes.

Blue/white is for the main beam as said previously but should go direct from the dip-switch to beside the right-hand headlight i.e. it shouldn't be visible near the mass of bullets by the fusebox, unless the harness has been cut open. PWs 2nd image looks like it could be by the headlight as at least two (should be three - blue/white, blue/red and black) of those wires are in a sheath.

White/green (you weren't sure of the colour) IS by the fusebox though, going to an in-line fuse with green/pink on the other side. That's for accessories which in this case includes wipers and heater fan.
paulh4

With no perspective to the location of the photo and given the wiring as it is I'd not guess it's located.

The sheathing *looks* to be newer than original and different one side to the other, but I could be wrong about both and as stated the blue/red cable isn't shown.

The spoon shape at bottom I wasn't sure about but it might be a loop of black cable.

The blue pre-insulated female bullet connector on the black cable has deep crimp marks yet the other two pre-insulated connectors don't, perhaps suggesting different people's work at different times but who knows.

All very strange and curious why this any of the 'work' was necessary in the first place, and near the fusebox.





Nigel Atkins

PaulW,
did you remember to clean the ends of the fuses too?

If you've not already done so, that blue/white really wants sorting even if not connected up for use (needs insulating and capped in some way if not used now).



Nigel Atkins

Paul

The age and state of the wiring including the connectors would make a new loom an attractive proposition in terms of reliability and fire risk. Sounds expensive but simpler in the long run for a car if a keeper.

Can buy direct from Autosparks (the manufacturer) and need to know chassis number and whether any changes to spec to what was fitted (i.e. did it have an alternator as a factory fit): https://www.autosparks.co.uk/finder/car/mg/mgb

The wiring looks old and bodged. You may find that once you start replacing dodgy connectors that you cannot strip back to clean enough copper wire.

If keeping going with repair and debodging:

A budget alternative to using the Lucas style [Lucar) brass bullets with the correct tool - https://www.vehiclewiringproducts.co.uk/p-273-bullet-crimping-tool?search=Bullets (which would be good to use these brass ones) is to use the W crimp version of Lucas bullets that are tinned steel (IIRC): https://www.vehiclewiringproducts.co.uk/p-453-w-crimp-type-4-7mm-bullet?search=Bullet and non-insulated crimp tool: https://www.vehiclewiringproducts.co.uk/c-1-home/c-51-crimp-tools/c-119-non-insulated-terminal-crimping-tools/p-270-diy-tool-for-non-insulated-terminals

These W crimp bullets are handy for fixing lighting circuits and low current stuff. Get rid of incorrect insulated bullets as others have said.

Lucas bullets and connectors: https://www.vehiclewiringproducts.co.uk/c-177-4-7mm-bullets-sockets-snap-connectors

Cheers
Mike
M Wood

Update well turns out that the wires leading from headlight to wiring loom was faulty and also the bulb had blown .the bulb was the old sealed unit and they cost £48.60 plus postage for one so better idea got two new headlights with halogen bulbs swapped these over.just handy I had in the house the wiring for a headlight got in for my triumph spitfire and never used it and its basically the same thing three wires and the three prong connector works fine just need to sort out the rev counter fuel gauge and side light drivers side again could be a bulb .
PW Creswell

Well done, even more progress.

I'm not surprised the headlight had blown given the unprotected wire.

With the side light it could be bulb but even if it is you want to test your sidelights (number plate and gauge lights) and indicators, hazards, brake lights with all switched on and going together plus main beam that way any poor earth connection(s) will show up. Hence keeping your battery in good condition and fully charged.

For the tacho and fuel gauge you'll need to continue working your way through the green cables and the connections. Do bear in mind the gauge voltage stabiliser needs to be wired correctly and at correct orientation and itself be earthed.

Nigel Atkins

"I'm not surprised the headlight had blown given the unprotected wire."

I doubt the two are connected, but never mind.

Also the fuel gauge will still work if it's not earthed just read high, or orientated incorrectly.
paulh4

Generally wires left bare like that are not a good idea as they're unprotected at that point so exposed to anything that gets there.

Look closely at the photo, there are certainly broken strands and possibly evidence of heat to the insulation wire covering, obviously we have no idea if these occurred before or after the blue bullet was (semi) attached.

It's no good applying a level of too much certainty to this car's wiring based on the very little info of the unspecified photos put up, other than it looks very messy.

PaulW also needs to know about the voltage regulator requirements whether the fuel gauge registers or not.
Nigel Atkins

PaulH,
I did think about whether I should put that - "I'm not surprised the headlight had blown given the unprotected wire" but on balance decided generally it being a warning about bare wires was in best interest, generally.

Plus it's not certain where that wire and connector actually are on the car, we can both guess but we don't know for certain.

You could and possibly/probably are right that it wasn't the cause of the blown headlight but there's no absolute certainty that it might not have been unless you know better, I don't mind being proven wrong.
Nigel Atkins

I certainly agree that bare wires and broken strands are not a Good Idea from a short-circuit and open-circuit/current carrying point of view, but exposed wires seems to work OK on power lines without blowing our houses up :o)

I'm not aware of any physics that says exposed wires will cause some kind of a power surge to blow a bulb, however if you have an intermittent contact (bare or not) that flicks on and off frequently enough then that will eventually blow a filament bulb as the switch on current for a cold filament is very much higher than the running current. For example the theoretical initial or inrush current for a 21w bulb is 24 amps, whereas the running current is less than 2 amps.
paulh4

Yes it was it being bare I was thinking of but more that it's unprotected in being exposed so that anything could get on it or touch and cause problems, the risk potential for issues being greatly increased.

One expose wire here, an unconnected loose connector there, who knows when they might be introduced to each other or other paths for the electric.

The blue/white wire also goes into what I assume (always dangerous) a blue pre-insulated connector of some kind that's without visible crimp marks in the photos so perhaps a loose connection there (and with reduced strand count) so perhaps giving variably connection and perhaps heat build up in effect giving perhaps a flicking effect to power getting through, a partial on/off, up/down to the bulb. or there could have been plenty of meat to the wires and connection and as was put unrelated to the bulb blowing.

Still £48 for a sealed beam, stocks must be diminishing, doesn't two minutes ago they were £16 for a set of two.

Certainly turning the incandescent bulb on regularly will shorten its life, and then turning off to cool down to turn on again, light being just about a by-product of the heat from the wire filament.

I don't like any exposed live connections, like those on the fuse box, or I suppose the battery post clamps but put up with them, I do wince a bit when I see metal tools being left on top of the battery though.
Nigel Atkins

So was down at the car today and while I was under dash trying to get tachometer working notice the ignition light was loose and when I moved it it sparked against the metal part of the holder for bulb also when car is running this light is still on? What would cause this to happen.

Thanks for looking regards Paul
PW Creswell

Have you got the wiring diagram for your car? The coloured diagrams from Advance Autowire in the USA are very useful as they cover most models of the MGB, both US and UK spec. Find them here and download them.
http://www.advanceautowire.com/mgb.pdf

The "ignition" warning lamp, marked more correctly as the alternator warning lamp on the diagrams, is not earthed but has one side connected to the alternator with a brown/yellow wire, and the other side to the ignition switch with a white wire.

When the engine is not running and the igntion is "on", power comes from the battery and earths through the alternator. When the engine is running, the alternator supplies a voltage equivalent to the battery voltage and so there is no potential difference across the bulb and it goes out.

If the light stays "on" either the alternator is faulty, or more likely, the bulb is shorting to earth. This might account for the sparks you saw.
Mike Howlett

What do you mean by ignition light was loose, the holder to the gauge, the bulb to the holder or the holder was hanging outside of the gauge?

Normally the light being on when the engine is running means the battery isn't getting charged (unless you mean running at slow idle).

A photo might help, this where phone cameras can be useful as they're easy to position and even if it takes a few attempts a reasonably in-focus photo can result.

ETA: Mike posted whilst I was still typing.
Nigel Atkins

https://youtu.be/zZsA0R1QZ8s

Link to video of ignition bulb sparking
PW Creswell

The casing of the bulb holder is live with the ignition on - engine running or not, which is why it's fitted into a plastic tube on the back of CB speedos and RB dashboards. So if you tap the casing onto an earth then yes it will spark.

There should be no voltage on the casing with the ignition off and the engine stopped, so if it's sparking then unplug the harness from the alternator. If it doesn't spark then the alternator is faulty, otherwise there is a wiring fault.
paulh4

PaulW,
it's as Mike and PaulH have put.

Why is the bulb holder so loose do you not have the plastic tubing?
Nigel Atkins

I guess that is what is missing and I bet that is one of those odd little things that you wont be able to get
PW Creswell

This is what it should look like on the back for a 68 to 72. If the plastic tube for the ignition warning light is missing and you can't jury-rig something you might have to get another tach, for the tube at least.

However there are 2-wire insulated claw-fitting bulb holders such as 37H5181 (image) that should fit a plain hole like the one for the night-time illumination. But the plastic tube extends to the back of the 'jewel' on the dial, which might complicate matters.

Or mount it somewhere else that is visible and insulated.






paulh4

Update plastic tube was on car but side clips must have broke off but some electrical tape and job done lights up then once car starts light goes out another problem to mark off the list
PW Creswell

Paul, well done

- but - I'd not rely on modern made electrical insulation tape as in my experience it tends to be crap and doesn't stick for long.

I'm not sure which clips you mean are broken but don't follow up the previous bloke's piss poor work with the same of your own.

Stray sparks are not a good thing and potentially can be extremely dangerous - all connections should be clean, secure and protected (properly).
Nigel Atkins

https://youtube.com/shorts/ke3-sAVvQRE?feature=share



Video of tachometer working needle going up and down like a fiddlers elbow lol but least it's working so now only fuel gauge and that wasnt working when I got the car
PW Creswell

Well done.

If you're lucky it might only be a connection causing the needle to dance, finding which connection might be another thing.

For the fuel gauge follow PaulH's diagnosis -

http://www.mgb-stuff.org.uk/electricstext1.htm#diagnose
Nigel Atkins

It's not easy to hear but it doesn't sound like the rpm is altering as much as the tach, particularly comparing 1500 rpm with 500. If it isn't then either the 12v and/or earth connections are flaky or its an internal problem with the tach. If you have an auto multi-meter with tach and dwell ranges that should help, failing that an analogue voltmeter connected between the points side of the coil and earth and see if that varies in the same way.

That link should help with the fuel gauge, although the reference to the stabiliser output is for the original units, if it is has been replaced it's more likely to be an electronic unit that outputs a steady 10v.
paulh4

BTW I've updated the text to include a reference to the electronic stabiliser.
paulh4

PaulH,
I might be wrong with what I think I'm hearing or perhaps you're listening on one of these mobile "smart" devices with tiny tinny speakers (I can't stand tiny tinny speakers) where as I'm listening on closed (shell) headphones, very old and humble ones though, and to me, and I could be wrong the needle is moving faster than the engine revs and the revs are reasonably steady except for that dip in revs which might want attention.

I've certainly not got the best hearing but I think I can also hear a child(ren) playing in the background.

There used to be two different sorts (IIRC two wire, three wire) and sellers of electronic stabilisers that I saw on on eBay but the last time I looked, a good while back now, both had gone.
Nigel Atkins

Plug-in, but still tinny.

As far as I'm aware like the original the commercial electronic replacement is also 'three wire' in that the can must make a good connection to earth for the stabiliser to function correctly. A long time ago I did see reference to a home-built electronic unit that reckoned it didn't need to be earthed.

Both mine are original thermal devices, if anyone has an electronic they can check if it needs an earth or not by unscrewing it from the firewall with the ignition on. If the fuel gauge goes higher, and higher still with the engine running, then it's a 3-wire. If reads the same under all three conditions then it's a 2-wire ... but probably still needs to be screwed somewhere to stop it flapping about.
paulh4

Paul,
I've got one of the three wire electronic units fitted to my Midget. IIRC I was going to bluetac it somewhere but there so little space and so many wires that it just hangs off its connections, been like that for 10, 12 years(?).

Probably find references in some Archives here as you said back then it wouldn't be as accurate in the cold (extremes of heat?) and you were right (about the cold at least, I've never checked in very hot weather) but the variance is no more noticeable than the variances of the modern made replacement gauges.

Nigel Atkins

https://youtu.be/_h13H4JMdyM

Another video of engine on idle and the rev counter still the needle is moving about a lot .just really trying to tune the car as best I can not easy trying to balance the carbs but starting to sound little better and goes along pretty good and at least i know the overdrive works
PW Creswell

To me it sounds a bit tapperty noise but that might just be tinny phone recording being near them, that idle seems very fast but again it might be the recording or me wrong.

Nice to see things tidying up in the engine bay.

It may be that even if there are poor connections and you find and cure them that the tacho itself needs attention.

BTW for overdrive on engaging and disengaging the car needs to be on load so don't (fully) lift your foot off the accelerator and don't dip the clutch pedal. See what it says and doesn't say in the Driver's Handbook about o/d operation.

To get the carb tuned (not that I'm any good at it) you need to first check valve clearances, points/plugs, timing and then mixture in that order, if you adjust anything in that chain you'll also ned to check the items that follow it in the chain.

You don't want to be doing carb fiddling until the important systems and items on the car have been dealt like brakes, steering, tyres, suspension, horn, lights and windows.

Good luck.

Nigel Atkins

Nigel - picture? When you say 'three wire' do you mean three separate terminals or three wires on two terminals? The latter is common on the MG where the B terminal is used as a branching point for the green wire which daisy-chains onto the tach. With two terminals they are usually a 'U' shape which allows for the connection of a second wire to either terminal. If your third wire goes from the can to the body then it's earthed as it it were screwed to the bulkhead.

First attached is an original, with an adjuster screw. Second is an electronic, no adjuster screw, internal PCB 'wiring' visible, same 'TOP' markings (although unlikely to be necessary for an electronic unit), and the same two male spades on the B connection and two female on the I. There are other versions of this with four males, or one of each on each terminal, with the mounting tap underneath instead of on top.

As far as heat goes the stabiliser and the thermal gauges are independently heat-compensated.

As for the video still sounds 'rattly', more than tappets to me but subject to electronic interpretation. Not much help for tuning, although it seems to pick-up well enough. You just have to work through the instructions for setting-up valve, ignition and carbs.






paulh4

Paul, it's not a modern bodge poorly made fag packet silver paper innards type which the likes of Moss sell that looks like an original, it's an eBay purchase from years ago, a modern small black box type. I can't take a decent photo of it because it's in with the rats nest of wiring that MG considered good enough behind the dash and I know from experience beyond the capabilities of contortion for me and focus for my old digital camera.

It's a little square(ish) black cube with three connectors (rather than internally connected wires as I thought it was, that must have been another unit on another car).

It really was fit 'n' forget which is how I like parts to be, and I've forgotten it thinking it was a previous type on another car. Two green wires go to it and one black wire for earth, ring to gauge mount IIRC, I can't see as with so much on the car it's black against a black background with intense backlighting from the big yella fing in da sky.

I don't think it has a joint/branching point, it's on a Midget and I'm not sure if they did, I can't remember now.
Nigel Atkins

I doubt it will be relevant to many other people in that case.
paulh4

I think the one I have is no longer available, nor the previous one I had.

I've just looked and there are three others on UK eBay, not as well presented/finished as the ones I had.

https://www.ebay.co.uk/itm/282642726457

https://www.ebay.co.uk/itm/254122488000

https://www.ebay.co.uk/itm/254355444447
Nigel Atkins

Two of those are from the same source. I had found those and the other one and they all say they need an earth connection from the mounting tab, as well as it being needed for a heat-sink.

One of them says strange things like other devices "... will also require a higher voltage (at least 12v) to provide a stable 10 volt output". If a car that has this type of instrumentation doesn't have more than 12v when running then it has other problems.

Also "It will withstand 2-battery jump-starts", something the original never had a problem with. I've seen the same warning with some electronic ignition systems.
paulh4

https://youtu.be/UJtq3eykzYs

Car seems to be running a lot better and rev counter is now sitting steadily on 10 rpm. Paul4H the rattle sound is the fan might be the rubbers are needing changed just another job to do but for now car is pulling away and accelerates fine overdrive works great as well .And while we have great weather I'm just taking it out as much as I can .
PW Creswell

I think we suspected the fan grommets before.

But yes, enjoy it, that's what they are for :o)
paulh4

This thread was discussed between 17/05/2021 and 25/07/2021

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