Sounds like a ground problem.
Try turning the headlights on at night and look real close at the turn signal indicators on the dash.
If one or the other is glowing faintly, its almost guaranteed to be a ground problem.
But, that is a one way test. If you don't see the glow, it can still be a ground.
I have a test unit I keep handy for weird problems with cars trucks and boats.
Its a long piece of insulated wire with an alligator clip on one end, and an insulated probe on the other.
Long time ago, I ran across a roll of single conductor curly cord, and grabbed it. Made for a much neater test probe.
I hook the clip to a known good source of ground. If possible, I use the battery terminal its self just in case.
Then I turn on whatever is supposed to be on, and probe its ground leg with the tip of my probe.
Its basically an ice pick with thick wall shrink tubing over all but the tip.
You want to start with the closest ground point of the unit you can get to, and if it starts working, move back until it doesn't.
For instance with tail lights of the old style, I could often touch the top of the brass bulb end right where its soldered.
If the bulb lit, I would move back to where the ground wire goes into the socket.
Many times it would not light when probed there, and it turned out to be where the ground wire was crimped into the socket.
J.
