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MG MGB Technical - 80 LE Wipers won't work

I hope this is okay that I just start a new "narrowed down" thread for my last two remaining issues.

My wipers don't work. I remember in the past they would not "reset" themselves at the bottom which I always heard they should do. This was not a big deal since I didn't typically drive the car in the rain. However, they do need to at least *work* for inspection purposes.

I have the wiring diagram from advance wire and see the colors. But I can't seem to locate the wiper motor itself. Can someone shed some light on this for me? I'm sure I'll be in better shape once I can get to the harness to check it's feed from the switch.
Jeff Grant

Considering my brake lights and tach also don't work, and judging by the schematic they're all on the same G(reen) wire set of wires, I think this is the commonality.

I think I've confirmed no 12V at the green wire of the brake switch (under the hood).

I know my grounds in the trunk are good. I've also confirmed the two screw eyes of grounds under the hood that were attached by one screw as I drilled out the screw (it was heavily stripped from someone in the past I'm guessing) and connected ground with no success.

So where do these get power from? I've confirmed all 4 of the under hood fuses are good.
Jeff Grant

Jeff, way to go on the flashers ...

The wiper motor is located behind the glovebox. Right above the wiper motor is the 3rd major ground point ... clean and tighten while you are there - it services that dash instruments.

You probably want to just spend some time and check, clean and tighten the bullet connections under the hood and also under the dash ... especially for the green wires. 30 year old connectors tend to be corroded or loose or broken. That will probably cure a lot of the gremlins that are lurking about in the wiring.

If you have time, you might want to look at the fuse box and check where the connectors are riveted on. Be sure they are all still tight.

Try to get battery voltage on all of the green wires. That will probably cure the tach and brake problem.

You can jumper together the wires at the brake switch to see if you have brake lights. If you do, the switch is faulty ... and will need repair or replacement.

Good luck.
Pat Harrison

The wipers use a different branch of the green circuit for running to parking, so possibly the park feed has become disconnected. The park circuit is also quite complex and there could be a break in the circuit in a number of places. The green to the motor (possibility 1) goes via the park switch (possibility 2) and comes out on the brown/light green (possibility 3). This is connected to the manual switch via a harness plug (possibilities 4, 5 and 6) then comes out of there on the slow-speed (red/light-green) wire. If slow-speed running is OK everything from here back to the motor and its ground will be OK.

The green parking wire comes from a 4-way bullet connector. This has a wire coming in direct from the fusebox, and another wire feeding another 4-way bullet conenctor and from there several other components including the wipers manual switch. So again if the wipers run off the switch and simply don't park the feed from the fusebox to the first 4-way bullet conenctor must be good, which just leaves the wire coming from that to the motor, and the other places I have mentioned.
Paul Hunt


How did you confirm all the fuses were good? Did you check for power at the terminals that the green wires connect to on the fuse box? You can have good fuses and faulty corroded terminals. Did you check the power input to the fuse box?
After you check the fuse box, you need to determine which branch of the green circuit has failed and trace it until you find the fault.

I confirmed the fuses with a multi-meter set on resistance.

Here's up update!

I removed the connector from the wiper motor to confirm that it did not get 12V on it's solid green wire. I then ran a wire direct from the front side (of car) of fuse 4 directly to it. My brake lights immediately came to life along with my directionals!

I guess the turn signal switch has something to do with power. It strikes me as odd though that the directional arm would work while the car was in on the OFF Position. Is this correct? I agree that brake lights should though.

I think the wipers might work once I get the wire officially spliced in and not just sticking through the wiper side of the wiper harness. I'm going to put a 10 or 15 amp fuse inline as well, just to be on the safe side.

I know this is a rather "ghetto" way of doing this and I should find the actual cause of the green wire set not getting power, but this is an okay work around for now I think.

Side note, I started the car and the tach also came to life, as bouncy as it always was.
Jeff Grant

Jeff - there is a "proper" way and an "improper" way to correct your electrics. Adding a wire is the improper way. Sounds like a DPO took a shortcut along the way. If you don't spend a bit of time to sort out the issues, you very likely will always be struggling with gremlins in the electrics at a minimum and letting all of the smoke out of the wires at a maximum.

My advice is to blow up the wiring diagram from advanceautowire, print it out and laminate it - it is a good reference while sorting thru wiring. Kinkos and other places can do it for a few bucks.

Next, divide up the circuits and check each one against the wiring diagram. Take your time. The electrics in these cars is very straightforward if you methodically work thru it. As you check and verify a circuit, mark it off on the wiring diagram. Start at one end of the car and work to the other end. When you find something that does not match the wiring diagram, make a note of it (include where you found it and the color of the wires that are connected). Post your questions and someone on the forum will respond.

You likely will find that some of the wires have either been disconnected or have been connected together and should not have been at one of the multi-junction female bullet connectors.

Something to keep in mind .... there is a method to the wiring colors in these old British cars.

Black --> Ground
Brown --> Not Fused. Hot all the time.
Red --> Fused. Running lights.
Green --> Fused. Hot when key is on.
Purple --> Fused. Hot all the time.
White --> Not Fused. Hot when key is on.

Pat Harrison

That's interesting. I assumed that brake lights and hazards should work regardless of the ignition key being ON, but you're saying that green is hot when key is on only. Is this correct?

As far as blowing up the diagram goes, I'm ahead of you there. It took 6 sheets of paper which I cut up in key areas and taped together.
Jeff Grant

Resistance is no good for checking electrics, it passes a microscopic current which may not be enough to blow open a bad conenction, or indeed close it in the case of filmed switch contacts. The only true test of eelctrics is to oeprate them under their design load, then measure the *voltage* at various points in the circuit. In an ideal world you will see system voltage at every component designed to receive it, but in practice there is always some volt-drop, and the volt-drop increases with current. Most circuits don't mind a bit of volt-drop - they just operate a bit slower or dimmer. Turn signals are very susceptible to bad connections, and so is the cranking circuit.

The hazards (like the main lights and some other things) work without the key in the ignition, the brake lights on an MGB only operate with the ignition on.

The turn signals should *not* work with the ignition off. If they do (and the hazards don't) it sounds to me like the turn signal and hazard flasher wiring has been cross-connected. The hazards have a brown (in this case fused with an in-line fuse just to be difficult) 12v feed to them, the turn flasher has a green. Both have a light-green/brown going on to the next partt of the circuit, but despite being the same colour these are electrically different, sounds like you could have these two swapped over. The loom wrapping should indicate which goes with which 12v supply wire.

If connecting another green supply wire to the wiper motor and the green that normally goes to the motor, then I'm not surprised that other things started working as your additional wire (only a diagnostic measure *please*!) will now be feeding everything on the wiper motor side of the break in the green circuit. Find the real problem, and fix that, don't strap odd wires in willy-nilly.
Paul Hunt

Correct !!!

Green is hot only when key is on.

Pat Harrison


Have you looked at the wiring diagram for your car? Easy to read color diagrams are available at click on stock schematics.

You answered the question on how you verified the fuses were good, but did you check the output and input terminals to the fuse box? If you have bad terminals, it won't matter if the fuse is good, you still won't get power to the green circuit.

By connecting a wire from the fourth fuse to the green wire to the wiper motor, you tested part of the green circuit and found that it is good. You need to look at a wiring diagram and find a common power point for the turn signal, park feature to the wiper motor, and brake lights. Looking at the diagram, the only one I could find is the terminal on the fuse box.
It is common for the terminals on the fuse box to corrode or become loose.

Use the wiring diagram as a road map and be methodical in testing. Make yourself a couple of enlarged copies of the diagram, one for reference and one to make notes on as you check the circuit. If you are methodical, you'll have the problem correctly diagnosed and fixed in less than a couple of hours.

An example of how to do this
1.) Use your meter and measure voltage to the wire terminal connected to terminal 6 on the fuse box. If you have power, then you know that the fuse box is good. If you don't have power, then you need to check to see if you have power to terminal 5 on the fuse box. Use a highlighter to trace the circuit you have tested and found good.

Check everything to see what is not working and what is working. Examples are fans, cigar lighter, etc.
The more information you have to begin with will help in identifying possible common faults.

A friend came to me when the radio in her Celica wasn't working. I asked her what else wasn't working. She said the only thing that wasn't working was the radio. The lazy b---h couldn't be bothered to try the power mirrors, wipers, heater, etc. It turned out almost everything wasn't working. Looking at a wiring diagram for her car, I found a common point of failure (fusible link) and had everything working in less than 30 minutes. Would have taken less than five minutes if she had bothered to check for herself what wasn't working and what was working.
The problem with her car was a corroded, high resistant terminal to the fusible link in the fuse box burned up. Replaced the terminal and all was well.


Okay Kimberly, I'm trying to take your advice on this one.

I investigated the fuses one more time, specifically the second one up (WN/G wire combo).

According to the schematics, the WN wires should be hot while the key is in the ON position. I did not have power on that side of the fuse. I took a jumper wire and placed it across from the WN side of that fuse to the number 1 fuse. My blinkers immediately worked just has they ahd yesterday when I hard wired into the green wire on the wiper harness.

I pulled off both WN wires as there are two attached. The one closest to the fender had upwards of 14V while the engine was running, the other had no voltage at all. The one with no voltage I traced to the ignition relay and was amazed to find it had no voltage there either but the car still started and ran fine. (comments on this??)

So I sprayed down both WN wires heavily with contact cleaner along with spraying the blade connector on the fuse block. Plugged them back in and still could not get 14V on that side of the fuse.

I swapped the WN wires around and still could not get power on that side of the fuse.

So all I can figure is that both WN male blades have separated from each other as well as from that side of the fuse in question. That's the only explanation I can think of to explain why neither blade will pass the voltage to the resistor.

I'm thinking about bypassing that portion of the fuse block entirely, even though it would make my engine bay wiring look like more of a mess than when I bought it.
Jeff Grant

You are barking up the wrong tree here.

In almost every case where two or more wires join together, like three white/browns at the fusebox, 12v only comes in on one of them, and goes out on the other two to other components plus into the fusebox.

I'm betting the spade you found 14v on had two wires in it? One will be from the ignition relay and the other will be to the ignition system, which is why the still engine runs with that spade removed from the fusebox. The separate white/brown feeds the in-line fuse for the cooling fans.

Put the white/browns back on the fusebox. Turn on the ignition and check you have 12v at both spades with white/browns on them, the fuseholder that side, the fuse cap that side, the fuse cap the other side, the fuse holder the other side, and both spades the other side i.w. where the green wires go.

If you have voltage on one white/browen spade but not the other, then the rivetted connection between those two and the fuseholder is bad, simply change the fusebox. Likewise if you have voltage on both those spades but not the fuse holder.

If you have voltage on the white/brown fuseholder but not the cap, then either the fuse holder is corroded (clean or replace fusebox) or the fuse is corroded (replace fuse). Likewise if there is voltage on one ene cap but not the other, or both end caps but not the green fuseholder.

If you have voltage on the green fuseholder but not on both of the green spades then again replace the fusebox.
Paul Hunt

To be consistant with most people on the board, the fuses are usually referred in order of top to bottom. The fuse with the green wires attached is considered the third fuse and the fuse with the purple wires attached is considered the fourth fuse.

Since you stated that one of the white/brown wires had power when the car is on, you should have power to the green circuit. With the car off, use your meter to check for resistance between pins 5 and 6 on the fuse box. You should have continuity. If you don't, the green circuit won't get power. Having an enlarged copy of the diagram makes it easier to read the pin numbers on the diagram. Where are touching the probes on the fuse box? If you have determined that the white/brown wire has voltage and you try to measure voltage at the fuse or the clip holding the fuse and you don't voltage there, then the fault is between the terminal of the white/brown wire and the fuse. The result is a bad fuse box.

According to the wiring diagram there are suppose to be three white/brown wires connected to terminal 5 on the fuse box.
1.) Incoming power to the fuse box from the ignition relay. It should have 12 volts when the car is on.
2.) Outgoing power to the radiator fans. It will not have power when the car is on unless it is connected to the above (1). This wire maybe missing from terminal 5 due to previous owner wanting to make the fans operate all the time or because there is a problem with the relay. It is possible that this wire is now being used to supply power to the third fuse.
3.) Outgoing power to the distributor. It will not have power when the car is on unless connected to first wire (1). This wire maybe missing from the fuse box due to changes made in the ignition system. Possible changes could be a non-stock electronic ignition system or someone made changes to avoid run-on. It is possible that this wire is now supplying power to the third fuse.
To be sure, unplug the white/brown wires from the fuse box, with car off, check for continuity between the terminal on the white/brown wire going to the ignition relay and the white/brown wires going to the fuse box. Label the wire coming from the relay. Then check again to see if the white/brown wire has voltage when the car is on.

Time to check the ignition relay.

Unplug the white/brown wires from the fuse box, making sure they don't touch anything. Turn the car on, motor not running. The white, brown, and white/brown wires should have 12 volts.
With the car off, only the brown wire should have 12 volts. The black wire should be connected to a good ground. If the black wire is not connected to a good ground, the relay won't work.
Make sure the relay is connected properly. You'll see numbers by the pins.
pin 85 - W2 - black wire
pin 86 - W1 - white wire
pin 30/51 - C1 - brown wire
pin 87 - C2 - white/brown wire

If the relay is at fault, replacementa are available for less than five dollars at most autoparts stores. Ask for a generic 30 amp Bosch style relay with four pins. For future reference, the same relay is used for the starter relay.

If you are not getting 12 volts on the white wire to the relay when the car is on, then the fault is between the relay and the ignition switch.

If you don't have 12 volts to the brown wire regardless if the car is on or off, then the fault is between the relay and terminal 7 on the fuse box.

If you have 12 volts to both the white wire and the brown wire when the car is on and you don't have 12 volts to the white/brown wire, then either the relay is at fault or you don't have a good ground.

Follow the white/brown wire that does have power and see where the previous owner spliced it into the car's wiring. By not utilizing the relay, power for the green circuit is going through the ignition switch and could eventually contribute to its failure.

The fourth fuse is constant power, not switched power. If you use a jumper to connect pins 5 and 7 on the fuse box as your fix, your temp gauge, fuel gauge, tach, induction heater (if still equipped), and possibly the dash brake light will never turn off. And if you put your car in reverse when you park, the backup lights won't turn off.

Some basics

What is the relay? With stock wiring, you have two relays. They both should have brown and white/brown wires.
The relay is an electrically controlled switch that connects the brown wire to the white/brown wire. The brown wire is input and the white/brown wire is output.

How to read a schematic.

It is important to know the flow of electrons so that you will be able to identify the input and output wires in a connection or splice. Terminal 5 on the fuse box is being used as a splice to connect the white/brown wires together.

A wiring diagram is a road map with only one-way streets. You start at the positive terminal on the battery and go towards components (lamps, motors, etc.). Along the way you are going to come to forks in the road (splices). Keep track of what is the input to the splice (connection) and what is the output.
To get you started with the diagram, you have a wire (battery cable) that goes from the positive terminal on the battery to the starter. The starter connection is a fork in the road. The battery cable is the input and the brown wires are the output going in several directions. Each being a one-way street going away from the positive terminal on the battery.

Thank you Paul and Kimberly for your advice.

I think the issue might be with the fuse block itself, but I'm going to try and troubleshoot with some more cleaning before replacing it as an "easy fix".

Suggestions on cleaning these corroded parts? It looks like the Statue of Liberty with all the green stuff on all the pieces.
Jeff Grant

Kimberly - great set of diagnostic steps.

Just to toss an extra bit of info ... I have run into a MGB wiring harness where there are only 2 White/Brown wires on #5 - one for the ignition relay and the other for the fans. The power for the coil was not a White/Brown on #5 but rather it was a white wire attached to W1 on the ignition relay (like late UK). It was a US harness everywhere else but it took more than a little while to figure out how the coil was being powered.

Jeff, as you disassemble, clean and reassemble connections, be sure they are nice and snug. Double check the color codes on the wires at each junction against your wiring diagram. When you get done, you'll have the electrics sorted out and should not have any electrical surprises for a long time to come.

Pat Harrison

Thanks for your comments Pat. I think you are right and that there are only two White/Brown wires on #5... one on each connection.

I won't get a chance to look at the car again until Monday. But by the looks of things, even if I have to put in an inline fuse myself for the time being, I'll be able to register/inspect the B next week!
Jeff Grant

Timely posting of Jeff's thread. Today, I took my MGB out and as ususal I test all electrics prior to heading off into the streets. OOPS, I have no:



fuel gauge

temp gauge


brake lights

I found two relays ( both mounted on the inner fender on the right hand side of the car )

the BLUE one, residing near the altenator forward of the fuse box has the following markings

87A, 87, 86, 85, 30/51 Lucas UK

this had a diconnected brown wire with a "melted looking" plastic terminal end. Also the 30/51 pin is rather loose in its "seat"

The BLACK relay is smaller in size and is located between(close to)the fuse box and firewall and has the following markings

87, 86, 85, 30/51 Lucas UK

All wiring apprears fine on the black relay. All fuses are new and their respective terminals have been cleaned.

I do not have a multimeter, so I cannot trace or test voltage. I will start with replacing the BLUE relay with the Bosch 4-pin unit and buy some terminal ends to repair the brown wire.

Hopefully Jeff and I will be back on the road soon.

Thanx to all for all the aformentioned advice. I will comment on my progress as I am sure Jeff will also


Gary :>{D
79 mgb


Progress... of sorts.

This evening I removed all 4 wires from the number 3 fuse on the fuse block.

I confirmed continuity between each male blade on each end, as well as between each blade on the other end while the fuse was in place. By the way, this is a brand new fuse.

I turned the car to ON while all wires were removed and confirmed 12V on one of the white/brown leads. I then attached that white/brown wire to the fuse block and confirmed voltage at the 3 remaining points.

Next I attached the other white/brown wire and successfully confirmed voltage there and at the remaining two points.

I then connected one of the green wires to confirm voltage. Now I had no voltage at any of the leads!! Definite issue here it would seem.

I unhooked that green wire and attached the other to confirm voltage. I had voltage at all 3 wires as well as the remaining male blade on the fuse block.

I attached that first green wire again to have voltage nearly disappear (<1V) from all the leads.

Of course, that green lead appears to be the one that does my brake lights and wiper motor. I had my wiper motor unhooked since my original hard wired power test. I touched the seemingly faulty green lead to the always hot side of fuse 4 and the wipers moved (as it did when hot wired to power).

I attached an inline fuse between the hot while ON white/brown to the problematic green wire and got no voltage, thus eliminating the fuse block entirely.

I checked resistance between that faulty green wire and ground while it was unhooked from the fuse block and the car was completely OFF. It read around 100 ohms. I think this is the issue... a short to ground somewhere.

Can anyone give some suggestions on this??
Jeff Grant

I was hoping someone could give me some advice today. This is the last thing keeping me from getting plates.

It would seem I have a short to ground which is sucking up all the power. But not enough to pop the fuse and not enough to melt wires.
Jeff Grant

So I investigated the issue a little more this evening.

I decided to give up briefly on the stock white/brown wiring supplying power to my green wires. I attached an inline relay to the always hot side of fuse 4 and directly into both green wires which are normally on the other side of fuse 3. Everything came to life, as expected (or hoped?).

The only downside of this approach is that the green circuits are hot at all times, instead of just while the car is turned to ON. I think that if I end up using this alternate wiring method, I'll add a relay switch in the passenger compartment to turn it on and off... or use the hot while ON side of fuse 3 to trigger it.

I had an idea though. What does anyone think about the ignition relay being a little weak and not able to supply enough power to drive everything on the green circuit? This would explain the fuse not popping if the green circuit was partially shorted to ground.

The relays are definitely original to my ownership of the car. I'll pick one up tomorrow if I get time to try out since they're cheap anyway.
Jeff Grant


your solution does not solve your problem. In fact, you will be adding additional points of failure to your electrics.

It is possible that the contact points in the relay are burned and pitted and are not allowing enough current to pass. Strickly for testing purposes to eliminated the relay, you could just jumper the #7 fuse connector to the #5 fuse connector - just don't leave this jumper in place - remove it after testing.

However, you have already taken a big step in identifying the problem circuit. You just need to take the next step.

First, reattach all wiring to the correct and original locations.

Before going any further, under the hood, locate the GREEN wire that connects to the induction heater on the carb. Disconnect it and position it so it can't short out on anything.

With the KEY ON, check to see if your have 12v on both GREEN wires at the fusebox. If not, disconnect the green wire that is causing the problem. Then, get to work and identify every component on the GREEN circuit that works (and also what does not work). If a component DOES NOT work, check the GREEN wire at the componete with your meter to see if you are getting 12V on the GREEN wire to the component. This will let us know that the component has failed but the wiring is working as it should.

If you have not done so already, get under the dash and locate all of the places where GREEN wires are connected via bullet connectors. Use your wiring diagram. Make sure that only GREEN wires are plugged together. I have found where someone plugged a ground wire into one of the 4way bullet connectors before which effectively disabled everything on that circuit. Do the same thing under the hood. I think you will find 1 4way connector over near the charcoal cannisters.

Unplug the wiring connector going to the wiper motor (just in case the motor has shorted internally).

Plug back in the green wire that was giving you problems and see if you have voltage on both green wires now.

OK .. turn OFF the KEY, reconnect the wire to the induction heater.

At this point, if you are lucky, then you have a good idea of what is causing the short.

If you don't, then here is the next step. It is not hard but does take a few hours to complete the task. That is to check continuity on each GREEN wire. How you ask?

First, make you a couple of long (15 feet or so) extension cables for your meter. Next, since you know where all of the green wires are connected now, disconnect all of them (at the bullet connectors, from the back of the gauges, from the fuse box, etc.).

Now, pick a GREEN wire. Connect one lead from your meter to the wire and connect the other lead to a good ground on the body. No reading? Good, that means it is not shorted out. Now, leaving the test lead attached to the wire, take the other test lead and seek out the other end of the GREEN wire using continuity (that is why you need some really long test leads). Once you have found both ends of the wire, label them. That completes one wire. Repeat until you have checked all of the green wires.

Once you have completed checking all of the wires, you should have either proved that all wires are OK or you will have located the wire that has a short.

Plug all wires back in.

A rambling thought. The other place I have found more than one short on the GREEN wires is on the transmission wiring harness which has the GREEN wires going to the reverse light switch. There is a metal cable guide where the the cables just love to chafe until the wires are exposed.

Let us know what you find.
Pat Harrison


While you are getting a new relay, pick up a test light. A test light looks like an ice pick with a wire attached. A test light will tell you if there is voltage, just not how much. You said the fuse is new, that does not mean the fuse is good. A test light can be used to determine if the fuse is truly good.

I removed the number 4 fuse while the car was running and it continued to run. I suspect that there has been some funky wiring done in the past by prior mechanics.

I have four inline fuses under the hood as well, but the wire colors aren't very helpful to determine which circuits they effect. I did confirm they are all good fuses though.
Jeff Grant

Changing the ignition relay resolved my problem!

Thank god, now I don't have to worry about finding all the wires on the green circuit.

Hope others besides myself have learned from this and will start with a "worth a shot" idea like this when someone else runs into this issue.

I'm going to change the starter relay as well because it's just as old as the ignition relay was.
Jeff Grant

Jeff Grant wrote: "I removed the number 4 fuse while the car was running and it continued to run. I suspect that there has been some funky wiring done in the past by prior mechanics.

I have four inline fuses under the hood as well, but the wire colors aren't very helpful to determine which circuits they effect. I did confirm they are all good fuses though."

The ignition system is not fused, therefore pulling any of the fuses will not stop the car from running.
If you want to know what the different colored wires go to, look at the wiring diagram.
Three of the inline fuse holders are for the hazard lights (brown wire), radiator fans (white/brown wire), and the anti-runon valve (slate wire). What are the colors of the wires going to the inline fuses?
To see what each fuse goes to, use a highlighter to trace each wire from the fuse to its component on the digram.

From everything you described above, I don't think that there is any funky wiring.

I didn't realize duct tape was part of the original wiring, that's why I thought they were out of the ordinary. Also, two are blade fuses, not tube fuses.
Jeff Grant

If I recall, they looked like non-factory wiring wires going to them, but if I find any that look stock, I'll refer to the diagram and post back if I can't find them.
Jeff Grant

"Next I attached the other white/brown wire and successfully confirmed voltage there and at the remaining two points.

"I then connected one of the green wires to confirm voltage. Now I had no voltage at any of the leads!! Definite issue here it would seem.

"I unhooked that green wire and attached the other to confirm voltage. I had voltage at all 3 wires as well as the remaining male blade on the fuse block."

A clear and step-by-step process that proves there is a bad connection in the 12v feed to the fusebox from the white-brown. With no load from the greens there is no volt-drop in the bad connection and so you see full voltage on the white/browns. As soon as you connect a load all the voltage is dropped in the fault. It also indicates that the ignition is getting its voltage from the white i.e. ignition switch feed to the ignition relay i.e. as per late UK cars as Pat says and not as the diagrams show.

This is a classic example of how the only true way to check electics is by voltage measurements *while they are under their design load*. Resistance and current measurements outside of that prove nothing.

In your case the bad connection seems to have been in the relay, or possibly in the connections to it, which may well have been disturbed enough while changing the relay to give a good connection with the new relay, in which case refitting the old relay would give equally good results now!
Paul Hunt

Duct tape and blade fuses aren't original. I didn't recall you describing that earlier.
There were inline fuse holders that are original located under the fuse box.
Have you figured out what doesn't work if you pull one of the blade fuses? Knowing what the fuses are for can help in identifying what circuits they protect. If possible see what is the color of the stock wires they are connected to.

Once figuring out the relay was at fault, I registered the car on Friday and got insurance/plates for it. I've driven it about 60 miles so far.

Aside from Friday evening when I took it's first 20 mile ride, it's been running very well. That first 20 mile ride though, my tach became very bouncy and finally dropped to 0 along with all power in the motor. I reseated the coil blade connectors and made it home. Then I sprayed them down liberally at home with some connection cleaner and the tach has been fairly solid since. I remember, years ago, that the tach always "bounced" some, but nothing that was overly noticable in the response of the motor. The tach is now smoother than it ever was in the past.

My speedo, on the other hand, is bouncing a good 5-10mph depending on speed of the car and load of the motor.

All other gauges are working properly.
Jeff Grant

A bouncing speedometer can be indicative of a dirty or binding speedometer cable.

It's bounce depends on the *load* on the motor? My first thought that wasn't possible, but if the engien moves under heavy load and the speedo cable isn't fastened to the gearbox properly (or that cable to the angle drive or the angle drive to the gearbox) then I suppose engine movement i.e. under load could affect the speedo.

Bounce can also be caused by a dry bush in the speedo head. If it bounces in time with the odo moving it will be the speedo head, if several times faster than that then it will be the cable, which could have broken strands as well as be dry.
Paul Hunt

I'm not overly worried about the speedo bouncing. It's slight, only about a 10mph sweep at most.

However, I'll note that my trip reset button doesn't reset the trip anymore and typically causes at least the trip to stop moving entirely. I don't know if this could be somehow related to the bouncing, but I suspect not.
Jeff Grant

Well it could be. If the wheels are jammed for some reason, then when the rotation of the cable tries to advance them but can't it will put more load on the cable. This will cause the slower rate of bounce rather than the faster rate. Not a good idea to let it do this as the odo mechanism will probably be jumping teeth as well which could permanently damage them.
Paul Hunt

Kimberly, et al: I bought a test light. Discovered the following:

Two of the brand new fuses were no good

Replaced ALL the terminal end fittings

Wire brushed and sprayed contact cleaner on all terminals at the fuse box

Replaced ALL fuses after cleaning fuse box contact surfaces

Everything is now working well.

Jeff Grant: You may want to do the same even though you seem to present several other issues related to your very car. Let us know how you fare

Thanx to all


Gary :>{D
79 MGB

My car's all set now. I've driven 220 miles and successfully passed the safety inspection here in MA replacing my old sticker which expired in September of 2002.

Thanks everyone for your assistance. I'm sure I'll end up with more questions as time goes on.
Jeff Grant

This thread was discussed between 17/06/2008 and 09/07/2008

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