Electrical problems: instrument panel and headlights.

[Cyman]

I need help trying to diagnose an electrical issue in my '97 850 turbo (157k miles)

My headlights, turn signals, hazard lights and instrument panel will malfunction intermittently. It only happens after the car has been driven for at least 10 min, but sometimes takes 25-30 min to manifest.

Here are the symptoms:

My headlights don't turn completely off, but they get VERY dim. to the point that I can barely tell they are on at all.

If I turn on my turn signals/hazards the lights don't turn on. I can hear the turn signal "click" from the instrument panel, but it goes off very quickly and erratically

All gauges on my instrument panel go dead as well as the Info screen at the bottom that shows mpg/ambient air temp, it also resets all data when it comes back on.. like it would if I disconnected the battery. the only warning light that comes on is the one that shows I have a malfunctioning light.

If try turning on my high-beams the engine dies.


sometimes the symptoms only last for 1-2 seconds, other times I have to turn the car off and restart it.. but it seems that once the car is warmed up the frequency of these episodes goes up.

also, it seems it happens much more frequently at low speeds or when I'm approaching a stop light. I can drive for 35 min on the highway without incident but as soon as I get back on city streets it will flake out almost immediately.


I have fiddled with relays and checked the grounding wire connections/battery terminal. I'm thinking that it might be the ignition switch, but I've shaken the key and it never causes/fixes the situation. I can't seem to get the symptoms to replicate when I'm at home trying to diagnose it. they always happen on the road.

any advice would be much appreciated (:

[rspi]

My guess would be that the alternator is bad. Not giving you proper voltage at low rpms.

[Srini850]

+1 on the alternator. I had a similar thing happen on an E36 BMW when my alternator went bad. Not to the same effect as your symptoms but headlights would dim, the car was losing power every time the turn signals came on and when the car was running at lower rpms. Right after the alternator died, my car shut down the lights, then the guages, then the battery finally cut the power to the injectors and I had to pull over to the side of the road. I would look into repairing this as soon as you can.

Go to advance auto parts or autozone. They will check your alternator and battery for free.

[jblackburn]

Autozone, Advance, Sears, etc. will do a free battery/alternator test for you.

See what voltage you're getting from the alternator.

Another possibility is your positive battery cable overheating - I had a car that did very similar things to this when its current flow was being pinched off by a bad cable.

[Cyman]

I considered a bad alternator at one point, but I'm not sure why the voltage would drop and seem to stay that way for as long as it does. sometimes even if I turn the car off it will still be this way when I turn it back on. also, the interior lights don't seem to go dim and the radio keeps playing like normal.

I suppose it wouldn't hurt to pull out a voltage meter and hook it up for a while. it's a free test (:

as for the positive battery cable: how would I diagnose it if this were the problem?


thanks for the help.
-Cyman