As long as I've owned my F100, the front driver's side marker light (under the headlight in the grille) has never worked. I've replaced the bulb, and still nothing. Also, the driver's side turn signal indicator stays on solid whenever the headlights are on, and I've always assumed that this was a dead bulb indication feature to alert the driver that there's a bulb out. Is that correct, or am I dealing with two separate issues here? The turn signals all operate properly, and the indicator does flash when the left side is on.

The previous owner had hooked up some driving lights and spliced into the marker light circuit to power them (and again, when I bought it, the driver's side didn't work...). I removed the splice and repaired the original wire, but that didn't fix the marker light, so the break must be some place else. I could very easily tap the driver's side to the circuit on the pass. side, but that wouldn't resolve the dash indicator though, would it? Aside from just tearing into the wiring harness, is there a likely spot to look for a loose connection or a blown fusible link? Thanks!

 

That's feedback, which means there's a ground issue somewhere. 9 times out of 10, it's an issue with the socket. Unless there are other glaring issues, the socket is usually the first thing I clean or replace. For the $7, I think it's worth playing the odds.

 

Yeah, I don't know how I didn't notice it before, but the ground tab on the socket is missing. I'll put that on my list for the next time I'm at the junkyard.

Thanks!