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Please help me figure out this electrical problem 700 1991

Here is a bizarre problem:

When the headlights are on, the lights that illuminate the speedometer, etc., do not work. The little lights for the high beams, bulb sensor, parking brake, etc., all work, but the dash lights don't. EXCEPT that when I turn on the taillight fog lamp switch AND put the car in reverse, the lights come on, including a steady left directional arrow (no right). If I turn off the fog lamp switch, the lights go out, or if I shift out of reverse the lights go out.

In addition, the lights on the center console where the shifter is do not work, nor do the little lights in the seat heater switches. I can't make them come on at all.

Just recently, a mechanic replaced the switch/device that controls the fan - it worked only on off and 5 and now it works on all speeds. Could this have messed something up while he was in there?

If there are grounds that are corroded or loose or improperly placed, can you be specific as to what ones I should check and where they are? Thanks a lot. I would love to solve this frustrating problem.
--
Darius in Albany NY '86 744 GLE, 91 745T








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    Please help me figure out this electrical problem 700 1991

    If you told me the problem came up immediately after the mechanic fixed the problem with your heater fan (resistor pack, yes?) then I would take it back to that shop and explain what happened. It's possible the tech accidently disturbed a ground, and somehow the taillight fog lamp and reverse lamps are completing an incomplete ground that serves the dash lights. The dash light circuit probably functions with only one ground, and that has been lost either through corrosion or the tech's mistake.

    You could probably skip the troubleshooting by ferreting out the hot and ground sides of the dash lighting circuit where-ever it's accessible, and then simply install a new ground spliced into the old ground. That's what I'd try first.

    If you check a manual you will probably find that the dash lights are grounded at the passenger footwell, behind the Fuel ECU. These are simple push-on connectors, and if you find one disconnected that may be your hint. Otherwise make sure the connectors are tight and clean if you do end up hunting around that area.

    -Dylan








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    Please help me figure out this electrical problem 700 1991

    Albany=salt=rust=corroded grounds. See the FAQ under Electrical Circuits for a complete discussion of corroded grounds.







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