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Re: electrical mystery
You've probably got a problem with the ground return for the dash lights.
Whenever one light source is powered it gets its ground through the fil-
aments of the unenergized lights. It will not cause any failure to occur.
You can trace the faulty ground down from the wiring diagram for the car.
I actually use this trick to get my side marker lights to flash with the
turn signals. If you connect the ground for the marker lights to the
hot side of the turn signals the marker lights will be illuminated with
the headlights, getting ground through the multiple lower resistance
turn signal bulbs; then when the turn signal is powered the voltage diff-
erence across the marker lights becomes very close to zero and the lights
go off. When the headlights are off the side marker lights will flash
at the same time, getting powere from the "ground" side and ground through
the other lights in the parking light circuit.
You might want to give your car a once over for ground integrity, which
is probably more of an issue under the hood and in the trunk than in the
passenger compartment. Corrosion can cause flaky grounds, which can
exhibit themselves as a number of funky problems. I pull off the ground
lugs and remove any oxidation with very fine sandpaper. I also scrape
some paint off of the body around the area where the lugs bolt down to
ensure that the threads of the bolt aren't the only things that are pro-
viding a connection. After I'm done I spray the ground lug with a battery
San Jose, CA (USA)