1978 F150 brake light/blinker problems

[Montiehall]

Hello all, I just bought a 78 F150 and i am having electrical problems. I am getting 12 volts to the brake light socket when both bulbs are out but when I put one bulb in the voltage drops to 5v and the bulb won't light. As soon as I pull the bulb out the voltage goes back to 12v . Made new harness for rear amid still same problem.

Any help would be great before I just take it all out.

I just replaced the wiring from rear to firewall and still same problem.

Well I found the problem to be power drop from fuse box to brake switch. I ran an in line fuse from Batt to switch and everything started working.

 

[Johnsbelljr]

Hello all, I just bought a 78 F150 and i am having electrical problems. I am getting 12 volts to the brake light socket when both bulbs are out but when I put one bulb in the voltage drops to 5v and the bulb won't light. As soon as I pull the bulb out the voltage goes back to 12v . Made new harness for rear amid still same problem.

Any help would be great before I just take it all out.

I just replaced the wiring from rear to firewall and still same problem.

Well I found the problem to be power drop from fuse box to brake switch. I ran an in line fuse from Batt to switch and everything started working.

I am having the same problem. Although I do not see a voltage drop. But am willing to try anything.... Did you run a new power wire from battery to the brake switch on the pedal??
I am also having issues with the blinkers not working when the headlights or parking lights on....

Thanks' John