Electrical gremlin - please help!

#1

I have an 87 325 if that matters.

I lost the headlights (both high and low beams) as well as the brake lights spontaneously. The running lights and tail lights worked. This really sucked, because the problem presented as I was heading for inspection for a track weekend.
I checked every fuse and I replaced the brake light switch at the brake pedal while at the track with no luck.

I dropped the car off to have the diagnoses made by an actual mechanic (I am not electrically minded). The problem is that the brake lights and headlights returned spontaneously without any intervention by the shop. So, they never saw the problem, and are trying to find it.

Anyone have a clue? Could this be one of the headlight relays in the fuse box? It seems highly unlikely to me that this is simple wiring short (how could that take out both the headlights and brake lights, but not affect any other lights?)

#2

The brake and headlights are very separate circuits. Other than a problem in the fuse box I don’t see a common point of failure in my reading of the circuit diagrams.

#3

jlevie wrote:

I would go fetch your car. If there’s no problem, there’s nothing for them to find. Drive the car around until the problem re-occurs and then take it back to the shop.

Alternately, get yourself a multi-meter, pull out your Bentley, and ask on the forum for ideas where to start.

Since, per Jim, there are few common failure points for front and rear lights, I’d check your light switch first.

Check it’s leads with the multimeter and see what is hot and what isn’t. Now move the switch and see what changes. Take good notes. Then when the gremlin re-appears do it over again and see if anything changed.

#4

That was my take after consulting the Bentley maual. I hope I can reproduce the problem before I am at the track again.

Thanks for the responses! If I find the problem, I will definitely post up the answer.

#5

on the left panel, Links, E30 Resources, there is a link to the Electrical Troubleshooting Manuals.
cheers,
bruce