My new project has headlights but no dash lights. When I pulled the headlight switch, I found quite a bit of corrosion. I sprayed it with contact cleaner and gave it a good brushing, but that didn’t seem to help anything.
Is there any way to clean/fix the rheostat or is replacing the headlight switch the only solution?
Also, would it damage anything to jumper the headlight tab to the dash tab to bypass the rheostat and check if the dash lights come on?
There are two sides to the dimmer circuit. The inner slip ring and the outer wiper. You have to get both of them clean and free of corrosion. Examine the switch carefully, take a couple of pictures, and then disassemble the front part and clean all the contact areas with very fine grain sand paper or emery cloth.
Success! As I was troubleshooting last night and at a total loss as to why I had no power at the fuse panel, I decided to jumper 12 volts from my cigarette lighter to the panel to see if the circuit was good from there. As soon as I stuck a blade between the fuse and the fuse holder, the dash lights came on. I hadn’t even connected the other end of the wire yet.
Apparently I did have power at the fuse panel.
I pulled the fuse again, cleaned the fuse holder thoroughly with a wire brush, and pinched the metal pieces together with needle nose pliers. I put the fuse back in and everything worked.
you can easily jumper the instrument wires coming into the HL switch, or use a multimeter at the switch, and see if the current is making it’s way into the switch. I assume you’ve checked the associated fuse. A poor instrument panel ground will also isolate the bulbs and cause your issue.
BTW, the circuit breaker in the HL switch gets weaker over the decades of use. It’s a prudent precaution to replace the switch even though it has no obvious faults. NAPA sells the best quality reproduction switch that I know of. Of course a NOS MotorCraft switch is preferred.
Of course, installing a headlight relay circuit is a common upgrade that has several benefits aside from more visible headlights; weigh a relay, the current is bypassing the HL switch and you won’t have to worry about losing your lights due to an aging or faulty HL switch.