I've got a 1986 F150 6 Cylinder 300 and got the wiring diagrams from you all the other day. Spent the day digging around, tracing wires, cleaning connections, and etc. Here is the current scenario:

Headlights and taillights works fine.

Left blinker on driver side works fine.

Brake lights and the rest of the blinkers do not work.

When I put on the left blinker, it blinks on the driver side rear. While the blinker switched is engaged, if I press the brake light, the passenger side brake light comes on.

I've jumped the brake switch and still had to engage the left blinker to get the passenger side brake light to come on.

Does anyone have a next step for troubleshooting? I can tell where someone has spliced into the fuse box with inline fuses and apparently made a mess of the electrical system. I am looking forward to getting it straightened out, any and all help is greatly appreciated. Please let me know what you think.

 

This sounds normal to me? The turns and the brake lights are the same lights. The brake light switch and the flasher power both go to the turnsignal switch. If the switch is in the center, the brake light switch power goes to both rear lights. If you move the lever one way or the other, one light will stay hooked to the brake light power, the other light will be taken off the brake light power and connected to the flasher power so it can start flashing.

 

I follow that and see what you are saying. What seems to be the issue to me, is that the brake light only works when the blinker lever is engaged. If you press the brake by itself, the brake light will not come on until you engage the blinker lever.

 

It sounds to me like your turn signal switch is behaving poorly.... assuming all the wiring is correct and unmolested....

 

I agree, sounds like a problem with the turnsignal switch. Remember, the brakes do go through the turnsignal switch.

 

Thanks fellas, I think I'll replace that turn signal switch. I had a feeling that was the trouble as well after reading some other info.

 

I don't know if this will help, but on my 1980 F15O, I had front parking lights coming on with brake lights. And no turn signals. That was flasher needed to be pushed back in.

 

Check and double check the grounding of the bulb sockets first...lots of weird things happen as electricity looks for the easiest path... ~Bill