I own a 1978 F150 Ranger.

Hoping someone can help me chase down the problem here. My thinking is it's a bad ground.

When I drive in daylight, left/right turn signal works as expected... and indicator in the dash blinks on and off as expected.

BUT as soon as I turn on the headlights (or even half-pull, to turn on parking lights) the LEFT turn signal indicator in the dash remains solid ON. The marker lights in front/rear of vehicle are not on - only the indicator.

With headlights on, and right turn signal on, left dash indicator stays illuminated solid while right blinks on and off.

When I use left turn signal, left dash indicator blinks on and off.

Any ideas where to start? Is it indeed bad grounding somewhere between left headlight, left turn signal marker bulb, and wiring back into cab?

Disclaimer: the wiring is certainly not standard... has been pigtailed in several places, to power stereo receiver, power aftermarket tacometer... previous owner/s had their way with it.

TY in advance!

 

I'd be looking for bad bulbs in the left lights, front & rear. Check the left sockets too, they could be bad. I think you are correct, it is most likely a ground issue, but it could be in a few places.

 

Thanks for your reply! I got out the multimeter and found the issue. Not a ground after all, but the wiring to the bulb harness was reversed.

Here is a photo of the CORRECT wiring, in case anyone else finds this thread and has the same problem.

Harness RED to WHITE+BLUE (may be WHITE+GREEN on other side)
Harness WHITE to BROWN
Harness BLACK to BLACK




Turn Signal/ Marker Bulb Harness Wiring - 1978 Ford F150