I have a 1986 Mercury Cougar and its headlights don't work anymore. Neither does the dome light, the radio, the dash lights (including the turn signals), the key chime, the digital speedometer, or the clock.
There is a wire the goes from the fuse box (but which isn't fused) to the headlight switch that is supposed to be hot at all times. This wire is a thick wire and is black with an orange stripe. This wire has no voltage (sometimes maybe a millivolt if you trust the meter to that level), but from the fuse box to the switch it has continuity. Looking at the wire that feeds the box -- which is a black wire with a white stripe (according to my husband -- I'm not sticking my head under the dashboard!!! ;->), it also has no voltage.
However, if you grab the wire bundle that contains this wire in the engine compartment on the driver's side up near the a/c compressor and radiator recovery bottle, the wire will come back to life with about 12 volts through it. This sounds like either a short or loose connector in that area. But, if you then turn the headlights on, the wire will go dead. *It will stay dead until you shake the bundle again.*
My husband drives this car to work, so we've only got a little while each night to work on it. We're going to start tracing the wire in the engine compartment, and maybe jumper the headlight switch to see if that does anything different, but I was wondering if anybody had seen anything like this and if somebody might have an idea of what the problem might be.
Another clue: with the wire dead, if you turn the headlight switch on, and turn the ignition switch to "run," then pull the high-beam switch all the way back to "flash to pass," the headlights, the dome light and everything else will come on, but will go dead again as soon as you move the flash to pass back to regular high-beam (or low-beam).
Thanks for any thoughts you might have. PRose