It is my 66 Ford Mustang 289 with 38k miles. So, the high bean headlights stopped working when I press the floor button. The low beams turn off, there is the lamp in the dash that lights up but the high beams don't work. When I press the button again, the low beams also don't work. I have the parking lights on only. I turn the lights off, I wait around 30 seconds, I turn the low beam headlights on, and they work again. If I turn the high beams on again, the same problem re-appears etc.
I've sprayed dielectric grease on the switch inside the dash. (Now the headlights don't dim off anymore when the engine idles or is off anymore). I swapped the 4 relays in the floor between each other and it didn't solve the issue. What could be wrong? The wires on the headlights are also properly connected.
Have you done your basic electrical troubleshooting of the headlight and dimmer switches? If the setup is still stock there are no relays for the headights in a '66 Mustang.
No, I didn't test the dimmer switch... but the light on the dash lights on though but not the lamps
Might be a good idea. After all, if original it's nearly 60 years old.
@chucktobias I replaced them both, since they looked old. I even replace the dimmer switch connecter. Same issue. And someone has installed relays and a fuse box with labels that have been chosen arbitrarily. The fuse box says Made in USA with a lightening. I don't see any name of a brand. I pulled the fuses out one by one, and none of them do the headlights! The normal beams work, the high beams don't, but the light on the dash turns on!
If the electrical system is no longer stock you have to trace it out to see what's going on with it.
@chucktobias OK. Do you have any suggestion on possible causes of this?
See where the wiring for your high beams goes and take it from there. Unfortunately since it seems to no longer be stock a shop manual wiring diagram won't be of much help.