1979 F-150. Here's my situation. Had no taillights, brake lights, rear or front directionals, or backup lights. I had marker lights, plate lights, headlights, and front parking lights. I decided to install a brand new wiring harness for the rear lighting and all new bulbs everywhere. I have lights everywhere now but with 2 problems. When running lights are on the drivers taillight is on bright like the brake light is on, and there are no Drivers side directionals front or rear whether the lights are on or not. Everything else is working fine. At this point, do you guys think I need a new directional switch since most of the lighting on these fords goes through that switch? Maybe a short in that switch? Thanks everyone.


Ok, I got 2 new flashers, put them in and the directionals & emergency flashers work fine now with the running lights off. However, I still had the problem with the bright running light on the drivers side, and no drivers side directional with the running lights on. So just for kicks I tried putting the bulb in with the tabs going the other way in the socket, somewhat forcing it in there, and it SOLVED that problem. Running lights were all good, directionals all worked, brakelights worked, markers, platelights, headlights, front directionals all work fine.

Although the wire harness/sockets on the rear lights are all brand new, I think the manufacturer wired the drivers side socket incorrectly. The power to the running lights seems to be lighting the wrong filiment in the 1157 bulb, causing the running lights to be very bright. And the power to the brakelight/directional is lighting the other filiment, which is dimmer and not discernable because of the bright running light. I think if I swap the 2 hot wires to the drivers side rear lighting socket I should be able to put the bulb back in the socket with the tabs on the bulb going the correct way. Any thoughts anyone?

 

Turns out the new wiring harness drivers side socket was wired backwards by the manufacturer. Reversed wires, put bulb back in the correct way and everything works.