I have a 1978 Ford F100 and am having some turn signal problems. I turn my left blinker on and both the front and rear work properly. When I turn the right blinker on, all 4 signals flash, including the front and rear side marker lights. The left side blinks a lot dimmer than the right side when this happens. I just replaced my turn signal switch today because it was really worn, and still have the same problem. I am wondering if I just have some type of ground issue. Any suggestions?

 

I would check your left front turn/marker light combo and the rear left/brake combo/taillight. Sounds like one of the bulbs is installed wrong or some of the wiring is not right. Somehow your turnsignal voltage is getting onto the brown wire, which is the marker light circuit. The brown wire is right beside the other wiring, and if you look at the bulbs, you will see dual filaments inside. One of those filaments is the brown wire/marker light circuit.

You could just take the front bulb out and then try it, and if that didn't make a difference put it back in and take the rear bulb out and try it.

 

Thanks a lot, I will give it a try.

 

Wait a minute, I made a mistake. You said your left side worked properly. I should have said check the right side, that is the side that is messed up correct? Sorry.