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 - Electrical Woes

As a new MGB owner, I have quickly learned (from reading the web pages) that you are the expert of MG. If you have time sir, could you address this problem I am having with my 1979 MGB (stock except for the pollution items removed).

On occasion, I lose my turn signals, brake lights, tach, temperature and fuel gauges all at the same time. I have replaced the complete fuse block/fuses and cleaned all the contacts I could possibly clean - paying special attention to the green, white and brown wires. I have added another engine to chassis ground strap. I did find that when I lose the gauges and lights, if I turn the car off and turn on the windshield wipers, restart the car, 2 out of 3 times everything begins working again?? I have noticed that sometimes when I apply the brake, it will "kill" tach and subsequently the guages, etc. This problem is very sporadic. Sometimes it will occur 2 or 3 times in one day or not happen for couple of weeks. I really love the little MG, but this problem is annoying if not safe. Any suggestions would be appreciated. Again, thanks for your time.
Mike D.

Mike - all your symptoms add up to one thing, which you seem to have diagnosed yourself. All those items are on the green circuit, and the brake lights causing them to fail does indicate a bad connection which 'gives way' when faced with the additional load. Seeing as you have tackled the obvious items I would now recommend that you use a voltmeter to test at various points in the white and green circuits around the fuse-block. Bear in mind that you could have a bad connection (particularly with PO wiring) between wire and connector as well as between connector and spade. With the ignition on you should see battery voltage throughout so any departure from this at some point in the circuit will show where the problem lies. With intermittent problems like yours I have been known to semi-permanently wire in an analogue meter so I can instantly see the voltage at a particular point when the problem occurs. In your case, even given the replacement of fuse-block, I would start on the green there then move forward or back as appropriate. You could try jumpering the headlights to the green in your garage to apply an even bigger (but still safe) load in the hope that it will cause the fault to appear then you can test at will with your meter. Even if it doesn't cause total loss of instruments etc it may drop the voltage low enough for you to find the bad connection.

Good luck,
PaulH.
Paul Hunt

Paul - What is the relationship of restoring the guages by turning on my wipers and restarting the car? I'm just adding to the circuit load by doing that....one would think that would have the opposite effect. Anyway, that is the only way I can get things working. I will follow your test procedures. Thanks.

Mike
Mike D

Paul, what about the brake switch.
Tatty

Mike - what *does* restore the gauges - turning on the wipers (ignition on) or starting the car? Are you saying that starting the car *without* turning on the wipers (or vice-versa) *never* brings the gauges back? By 1979 the wipers had gone back to being powered from the green rather than the accessories position of the ignition switch and their own in-line fuse which would add to the load as you say, but maybe starting the car wiggles the bad connection and 'repairs' it. Interesting, but I would still go for the voltage measurements I mentioned earlier to find the cause.

Tatty - what *about* the brake switch? If you mean that the brake lights might be shorting out then I would expect applying the brakes to blow the fuse. The only time it wouldn't is if there is a bad connection in the green that 'goes' instead of the fuse, but that is what Mike (and I) is assuming is the problem anyway.

However, whilst looking for something else earlier today I noticed a change (early 78) in Clausager whereby thermal cut-outs were fitted instead of fuses to eliminate overheating of the holders, but he specifically states this is for 'line' fuses. Were they self-healing? Could they be more widely used than just line fuses? Could they be repairing themselves just as you turn on the wipers and restart the car?

PaulH.
Paul Hunt

Paul,

What I have to do to get the guages / signals working again is turn off the car, turn on the wipers and restart the car with the wipers on. I may have to do this several times to get things working again. I can then turn the wipers off and everything will work again for several days or sometimes just a few minutes..... Turning the car off and on doesn't ever fix the problem.

Mike
Mike D

Mike - really strange on the face of it, but maybe when you find the broken connection it will all come clear.

PaulH.
Paul Hunt

This thread was discussed between 20/11/2001 and 22/11/2001

MG MGB Technical index

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