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MG MGB Technical - Electrical gremlin....

Hi - my Dad's 1968 roadster has been standing for approx 2 years. Initially it wouldn't start, suspected fuel pump but turned out to be a case of simply removing the filler cap.

Anyway, got it going and noticed no fuel gauge reading and no rev counter. Indicators and brake lights also not working. The fuel gauge was definitely working last time it was started. Did some research during the week and discovered that all these are fed off the green circuit.

Put a new fuse in today, old one looked ok but corroded, and everything worked fine....for a couple of minutes. Pulled the fuse and it was fine so I sprayed some WD40 onto the contacts in the fuse box. Everything worked again so I took it out for a quick spin (obviously no MOT at present so this was just through my Dad's village, which is basically a cul-de-sac 25mph tops, before anyone shouts at me!).

Rev counter went a bit wild at first but settled down, thought to try the indicators after a couple of runs and the rev counter and fuel gauge died. After a short while they came back on but every time the idicators were activated the rev counter and fuel gauge died again.

I therefore thought I'd better ask advice, could this be a bad earth somewhere or some other problem??

Also worth mentioning is that the fuse box had no cover, I didn't have time to remove the fuse box itself and give all the contacts a good clean - presumably this would be a good place to start?

Thanks, Neil.

n r marchant

Neil. Most probable cause is corrosion on the two clamps for the fuse to fit into. Clean both sides, install the fuse, and test again.

Good job of trouble shooting the basic problem.

Les
Les Bengtson

Neil - I will second Les' recommendation but recommend that you use some good contact cleaner rather than WD40. Once the contacts are well cleaned, you can then preserve them with a light coating of WD40. Cheers - Dave
David DuBois

If once you got everything working the brake lights *didn't* cause the tach etc. to fail like using the indicators did, then the problem now isn't in the fusebox but one of the spades or bullet connectors further along one of the green wires.

There are probably four green wires at the fusebox on two spade connectors. One feeds the instruments and heater fan, one the wipers, one the brake lights and one the reversing lights. Only if *all* of these circuits are failing when you turn on the indicators will the problem be inside the fusebox, which as well as the fuse and holders could also be the riveted connection on the back that joins each fuse holder to its spades.

Remember you could have any number of faults affecting some circuits and not others, don't assume a magic bullet will fix everything.
PaulH Solihull

Thank you for the replies, much appreciated.

Hopefully a good clean will improve things, sorry about the WD40 but it's all there was to hand - it's in a pretty rural spot!

Might be a good idea to get a new fuse box cover, probably more sensible to get a new fuse box into the bargain. If that doesn't help I'll move on to Paul's suggestions.

The idea is to get it through an MOT and then back to my garage at home where I can spend some time on sorting any minor niggles and taking the old girl out a bit more regularly - weather permitting!
Neil_M

I had time last weekend to remove the fuse box and give everything a proper clean and apply some electrical contact cleaner. Everything seems to work fine now so it'll soon be booked in for an MOT.

Thanks again for all the helpful comments.
Neil_M

This might be off the track a little, but i was having problems with my pump, even bought a new one to no avail. It turned out that i had be sorting out the electrics in the boot and, well the pump earthed in the boot, using the bolts that hold down the number plate bracket. Re connected the earth and hey presto everything was fine. Just an idea.
Good luck
Gerry Lodge

This thread was discussed between 25/07/2010 and 15/08/2010

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