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MG MGB Technical - Electrical Fire

Well last night I was driving back from school, headlights on, heater was on, and I had the wipers on to get some of the moisture off. As I turned the wipers off I heard a disheartening silence. The heater fan had suddenly stopped as well. This can't be good, I thought to myself. Then I noticed smoke pouring out of the right hand side of the hood. I immediately killed the ignition, got the extinguisher out, and popped the hood preparing for the worst. Fortunately the fire was out already, and there was no need for the big red bottle. Well the culprit was a hot wire I was running from the fuse box (hot side) to an amp powering a subwoofer. The wire had gotten old, brittle, and the insulation had cracked, causing the wire to short itself on some metal, and really frying the wire. So here's my question. I pulled the wire off the fuse block and checked the fuses, they looked good. I hopped back in the car, and there was still no heater or fan. Great, I thought. So I checked the fuses again just to be sure, then I got in and tried again. Now the heater and wipers worked, but the turn signals were dead. All the lights worked accept for the turn signals. Well it was getting chilly, and I can live with out blinkers, so I high tailed it home. Next morning I go for a drive and the blinkers have come back to life. However towards the end of my drive the entire guage cluster fails. I fittled with the fuses some more and the guages came back to life. What the hell is going on. Is my entire electrical system going through Post-Fire traumatic stress syndrome?
Curiously
Bill
69 B-GT
Bill Mertz

Bill - replace the fuses and check the fuse holder clips to make sure that they are holding the fuses tightly. The clips in the holders could have lost their shape due to the heat caused by the overcurrent condition. The fuse may be hanging on by a thread and will make and break as you fuss with it.
Good luck - Dave
David DuBois

and add an inline fuse to that wire for the subwoofer!! If you have one already put a lower amperage on. If the fuse keeps popping go visit an auto electrician. In fact go visit one anyway, it'll be cheaper than burning out your B!
Ian Johnston

Bill,

As you've probably guessed by now, the Lucas fuse box is a pretty indifferent piece of engineering and has to be responsible for 90% of the 'Lucas is crap' reputation. It's worth your while checking it *very* carefully and making sure that the connectors and fuse holders themselves are clean and make good contact - an intermittent contact there can cause a fire itself.

Cheers,
Jim
Jim Aitken

I got one of those little wire brushes that looks like a toothbrush and used it to polish the contacts in my fusebox after removing the old fuses , installed new fuses and it seems to work better now .

I also used the electrical contact improver paste (ground copper) from Eastwood , painted on the fuse ends - I use it on pretty much every connection I touch anymore and it really helps .

-Nate
Nate

All those circuits are fed from the 2nd fuse up. By the sound of it your shorted wire was getting its supply via the spades on the hot side of the fuse-box and not via the fuse. A heavy current would have heated up those spades and the associated fuse holder, which may have caused an existing small high-resistance condition to become a big high-resistance condition. As well as the spades and fuse holders there are rivetted connections on the back, these can be soldered over, or the whole thing replaced.
Paul Hunt

This thread was discussed on 30/01/2002

MG MGB Technical index

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