MG-Cars.net

Welcome to our resource for MG Car Information.

Recommendations

Parts

MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG MGB Technical - Removing drivers seat + electrical problems

How do I get the drivers seat out of my late MGB GT? Its not detailed in the haynes manua. I want to mount the runners further back so Im not so close to the steering wheel. Im quite tall and the driving position is a tad uncomfortable at the moment. Im going to mount solid strips of metal (heavy gauge) onto the existing mounting points for the seat runners, then bolt the seat runners onto these strips of metal further back from the original position.

Another point as well. People really werent joking when they said MG wiring can be a nightmare. My overdrive is intermittent, my rev counter is intermittent, my dashboard lights are intermittent, my interior light on the console doesnt work and the heated rear window is intermittent. Im thinking its all down to frayed connections that need to be redone. I know the dash lights are because the rheostat is bunched so it will be getting bypassed. My favourite fault though is this... the brake warning light is on whenever the lights are on. Then I put on the handbrake, the heater control illumination lights up! Also, my rad fan has a switch as well as the thermostat. The thermostat has been replaced but the original one is still connected as well and is just hanging there loosely! Whoever did the wiring in this car (possibly Stevie Wonder) hadn't got a clue. This is all stuff to be tackled over the course of time. Main priorities are the seat, the overdrive and the dashlights. Anyone want to help??

Cheers,

Ross
R Kelly

Well, hello there Ross, and welcome to the dark side.

So, you have an intermittent rear window heater?? Well you’ll get no sympathy from me. I have to drive along with a big long rag and try to beat the steam off of my back window because mine is not heated at all.

But seriously, you just have a bit of sorting out to do. To bad you couldn’t have had your old car overlap a bit with the new one, but so be it.

I’ve seen the pics of your car, and it looks quite nice. At least you have a car that is nice enough that you don’t have to wonder if it’s worth fixing.

Your rev counter problem is likely not a problem with the rev counter. I think it is likely telling you that there is a bit of an ignition problem in the distributor. I think others will elaborate on this more than I can, and I will watch because I have the same problem myself.

If I had to guess on your weird electric crossover problems, I would put it down to some bad grounds in the car. Usually when I have seemingly unrelated pieces of electric equipment talking to each other, it is a bad ground somewhere. That might explain your brake warning light and heater lights, etc. For example, is your license plate holder tight? If not your fuel pump might quit. That’s the way it is with grounding.

The console light is likely a bit of dirt in the door button that turns it on. The dash lights are likely the rheostat, but if you bypass it, full bright is not going to be blinding.

If the overdrive works fine sometimes, and then not at others, it is probably an electric connection problem also.

It sounds like you need to spend some time cleaning up the electric connections in the car. It is loaded with bullet connectors, and pulling them apart and cleaning them could work wonders. Disconnect the battery before you start. When you clean them, watch out for female connectors that have lost their spring, or have corroded entirely. Clean up the places where the grounds meet the body. Clean the contacts in the fuse box, and put in new fuses. Do not look at the old fuses, just put in new ones. When you get done, you may find most of your problems, other than the seat, are gone.

As for your seat, I am kind of guessing here, but I’ll tell you what I think it was supposed to look like. My 68 GT was rusty enough that I didn’t really get a good feel for how it was originally. But, I think there were captured nuts in the floorboards that held the seat rails in. So, if you slide the seat all the way forward, you can remove the rear bolts, and if you slide it all the way back you can remove the front bolts. All this is done from inside the car. Because I had to weld new slabs of metal into mine I just have through bolts with the nuts under the car, but I think originally they were captured nuts.

Also, I think some aftermarket steering wheels stick it closer to your face. I think I have that problem with mine. I suspect the wheel is farther back than the original, so that if I get far enough back to make the wheel comfortable, I can’t get the clutch to the floor.

Keep a stiff upper lip and all that!

Charley
C R Huff

Thanks for the help. Dont get me wrong! I really like the car. Its great fun and to be honest Ill enjoy doing the bits and pieces here and there but theres just a few jobs I want to take care of up front on it. Ill try cleaning all the connections anyway and Ill probably end up replacing a lot of them. Car electrics are something Im quite good at. Ill leaf through my haynes manual this evening anyway over dinner and see where I should start.

Cheers,

Ross
R Kelly

Ross,

there are four bolts that hold the seat runners to the floor. Push the seat to the front and you will find the two rear ones, push it to the rear and you will be able to reach the two ones at the front.
Take care not to sheer off the captive nuts in the floor.

Before trying to find an electric fault at the OD, i would drain the oil from the gearbox and give a good cleaning to the OD filter first. A blocked filter and a low oil level are often responsible for the fault you mention.

With the wiring there are many possibilities what might be wrong. In most cases creative non car electricans are responsible for the problems.
On your car's modell year, the tach is not the same as used up to the early 1977 modells, so intermittand function does not mean that there is something wrong with the ignition system, it seems that it is simply a bad connection to +12 V or to the ground.

For getting every thing working, just try to rebuilt all the connetions to the delivery state of your car and take out everything that did not come with the car when it left the factory.
The Lucas wiring system is very simple if you have some additional information upon it.
For the colour sheme look here: http://englishcars.com/lucas.html
and for the coloured wiring diagram have a look here: www.advanceautowire.com/mgb.pdf
Scroll down the pdf to the last sheme(No.: 33) that shows the wiring for 1977 1/2 on cars and will give you an idea how your new baby should have been wired.

Ralph
Ralph

Thats great, thanks. Yeah I was thinking with the overdrive it must be low oil or the filters blocked. It sticks on or off and other times it will work fine. So 20w50 oil in the gearbox, yeah? (Same oil as I used in my '74 VW bus incidentally, but in the engine.) Thaks for the info about the electrical systems. I think it will just take me a couple of days to get it sorted out and it will be fine. As you say, its not madly complicated.
R Kelly

Ross,

An aftermarket wheel of smaller diameter can do wonders for seating and steering by allowing more thigh room beneath the wheel. Here is the one in the 70 B I care for, it is a 14 inch Tourist Trophy wheel. Since the BGT was discontinued early here (none after 1976), I'm not sure if the home examples received a smaller wheel, so measure yours first... I may be all wet!

Really good schematics for your car can be found at:
http://www.advanceautowire.com/mgb.pdf plus all sorts of neat relay kits to reduce the current going through the switches. Relays will result in more current going to the device and less degradation in the switches.

For instrument brightness, take the instruments out and clean the insides of their cases. You can paint the insides flat white if you wish. That helps.

The gentlemen above have correctly described the correct method of removing the seats, and the stray currents from poor grounds.

warm regards,
dave


Dave Braun

Yes, 20w 50 oil in the gearbox. Non-synthetic if it is an overdrive gearbox. And some folks like straight non-detergent 30w oil in the gearbox because it doesn't foam... especially in an OD gearbox. I've used both, and liked both, but the 30w was marginally better with overdrive.

Hope this helps,
dave
Dave Braun

I find it easier to remove the front seat rail bolts first (which always nead a spanner) then you can put the seat far enough forwards to clear the rear bolts and get a socket and extension on them. When lifting the seats out watch the lower half of the runners don't fall off at a critical moment and ding the paint.

It will probably be easier to drill new holes in the floor and move the existing runners back. If you bolt strips to the existing holes, and the runners to them, you will probably end up with the seat being at least 1/2" higher as well as further back as you will need space *above* the floor for the nuts or heads of the bolts in the runners. The front captive nuts are concealed in the cross-member so they are the problem ones if they shear/strip. The rear ones are accessible from underneath.

The most common cause of an intermittent OD is wear on the lockout switch on the gearbox. This is 'adjustable' by removal of one of the two (originally) washers from between the switch and the gearbox casing. The switch is awkward to get to, you have to undo the rtear crossmember to chassis rail bolts and lower the rear of the gearbox on a jack, and remove the centre arm-rest, pull back the tunnel carpet, and remove the small access panel on top of the tunnel. The OD switch is on the left-hand side (facing forwards) of the casing, the reversing lights switch is on the right and more accessible from underneath. Could also be a problem in the wiring to or from the gear-lever manual switch (which is prone to fracturing and shorting which can cause big problems as it is unfused). Eliminate electical problems first before bothering with the gearbox oil. This can be done by wiring an ammeter in series with the overdrive circuit. If this flickers with the overdrive switching in and out when it shouldn't the problem is electrical. If it doesn't it is fluid or mechanical.

The rev counter could be down to a bad connection on the 12v supply (green, fused ignition), earth (black), or sense wire (white/black from the coil -ve). Could also be a problem inside the tach electronics, or if it jumps up from zero to the correct reading with a sharp rap from a knuckle then it is a sticking needle.

If all the gauge illumination is intermittent together, and the rheostat has been bypassed, then there is either a bad connection in the red from the main lighting switch to the rheostat or the red/whites from the rheostats to the lamps. Could also be a bad earth, which is shared will all the lamps and courtesy light switch as far as I can see. You will need a voltmeter or test-lamp to see if it is the 12v supply or the ground missing before you proceed any further.

The courtesy light relies on 12v from the purple (fused always on) and an earth from the door switches to light when the doors are opened, or the same earth that feeds the gauge illumination when the manual switch is used. Could also be the bulb. There are two wattages of the appropriate size, get the lower one or the heat will melt the translucent cover.

The HRW is powered from the green to another white/black through the switch, plus another earth to the element. There are a number of connectors (bullet and multi-way) in this circuit any one or more of which could be faulty, so again you will have to track the voltage through with a meter or test-lamp.

The interaction between the lights, brake warning light, handbrake and heater illuminations sounds like a bad earth which could be the cause of several of your problems. As I say many of the components on the dashboard share the same earth, and if that is missing you will get these interactions. There is a main earthing point behimd the dash, high up in front of the driver. This feeds the wipers and heater fan first, so if these work OK and don't change as other things are switched on and off that should be OK. That then goes to a sealed multi-way connection with six other wires coming off it, one of which is the heater illumination. So as that is part of the problem it would seem that sealed multi-way connection doesn't have a proper earth. However there are no other connectors between it and the main earthing point, so it would seem there is a break in that wire somewhere.



Paul Hunt 2

Ross,

I think I remember that the seat rails have multiple holes in them. I might not remember correctly since I was not putting them back onto original floorboards and I was drilling lots of holes. But, if I'm right, you may be able to unbolt them, move them back, and rebolt them in a different hole set to the same captured nuts.

Sorry to lead you astray on the tachometer. I never had a "new" car like yours.

Charley
C R Huff

I did a bit of electrical work today. The problem with the brake warning light was just that the bulb holders were swapped around so I put them back where they were supposed to be. A lot of other intermittent problems are down to the awful switches in the car. The only one working properly is the fan switch. Im going to order some new switches anyway. I need a new clock as well. The old one isnt working at all. The rev counter seems fine now. It seemed to be the needle sticking. The overdrive is the next big thing. Ill see how it works out when I change the gearbox oil and clean the filter this weekend.
Ross Kelly

Does anyone know of a supplier that does aftermarket switches designed for the MG but of a better quality than the stock post 77 switches? I was looking on Sussex classic car parts website and the original parts are very expensive, and from what Ive seen are not good quality.
Ross Kelly

Ross, you could try cleaning out the interior of the switches. My GT was 7 years old when I bought it in '85 in the UK. Even then the rocker switches were full of vertigris. A good clean out & most of them are still in use today, 23 years on.
If you redrill the original seat runners, you can gain about 2" further back. Whether you can move the seat back far enough to fit the front bolts is another matter. This is something you'll have to work out whatever method you use. Barrie E
Barrie Egerton

On both my cars the holes are right at the ends of the runners. Whilst new holes at the rear would work when moving the seat back you would need new holes in the floor for the front holes. Unless you can move it back far enough to clear the fixed cross-member you are going to have fun attaching new captive nuts, but it can be done, as I found out when fitting a new floor without fitting the nuts first :o)

Hardening of the grease is the usual problem, so it becomes an insulator more than a lubricant, and the hazard switch is the usual victim as it is rarely used. The later illuminated switches are quite fiddly but even these can be opened up, cleaned out, and new grease used. However if the problem is wear I've not had much success tweaking things inside the illuminated switches, unlike the earlier rocker switches with larger bits and more room for 'adjustment'.
Paul Hunt 2

When I welded in new floors I welded around the front captive nuts before fitting the floor pan just so I never have to worry about them shearing in the future.

Also since you're taking the seats out you're going to have to put them back and I always find that the harder of the two jobs. I found the easiest way to get the damn things back in is to put two bolts through the rear captive nuts from UNDERNEATH the car. Then you have two studs protruding from the floor inside the car that you can slip the wood strips, aluminium spacers, and rails over. They hold everything aligned while you get the front bolts in then you can just unscrew them from under the car then screw them back down from the top.

Simon
Simon Jansen

Ross,

You are quite right; the original - and very expensive replacement - switches are rubbish! I would suggest you reduce the load on them as far as possible by using them to send signals to relays, which do the heavy duty switching.

Paul Hunt's 'Pages of Bee and Vee' give lots of useful information. Dan Masters in the USA markets kits of relays and gives useful advice regarding how to use them.

Hope this helps.

Peter
Peter Hills

I was actually thinking of fitting a bank of relays to be honest. Ill live with whats there for the moment though. Ive more pressing matters to attend to. Thanks for the advice everyone. Im thinking with the seats, my easiest option, and probably my safest option too is to go with the idea of the flat aluminium or steel strips and mount the runners onto them. That way also, I wont have to worry about remounting the seats to new fixing points.
Ross Kelly

This thread was discussed between 14/03/2008 and 18/03/2008

MG MGB Technical index

This thread is from the archive. The Live MG MGB Technical BBS is active now.