I'm working on my 76 f150. One day all the lights quit working. Everything gone, I couldn't find the problem so I started from front to back first. Actually first I replaced all the fuses, bulbs, and the headlight switch. Still nothing. I then cut the terminals up front for all the lights to check for volts, had em. I replaced all the terminals with new ones and had all the front lights. I thought the back would be just as simple. Not so. No volts at all at the lights in back. I looked around for grounds, corrosion, and anything I could find. Nothing also. I cut the wire harness at mid bed and checked for volts there. All well at that point. I made a new harness, ran it back and started plugging new terminals in. I got the left side first and checked that all was well. I have parking lights, signals, the marker and brake lights with the headlights off. I turn the headlights on and no brake lights...Wiring is not my strong suit and I was actually pretty pleased with the progress but this has me baffled. I did manage to hook some stuff up backwards at first and the brake lights worked in reverse, that is they were on until I stepped on the petal at wich point they went off. Hooked it up opposite and here I am with all lights, just not the brakes with headlights on. That is also to say that the brake light is not lit either with the headlights on, they just won't come on...any help would be appreciated.

 

Quick update. I hooked all the tail lights up and had them all working in unison except ofcourse for the brake lights with headlights on. Also noticed that the signals don't work when lights are on also. Was reading another post on stuck 4-ways and signals and my relay seems to work great when no lights are on but when I turn the headlights on and try to signal right or left I can hear the relay click ONCE and then it stops. I'm baffled...I know I'm close to the solution to all this but ugh!!

 

If the brakes and turns work ok until you turn the headlights on, then you have a ground problem to the rear lights. This ground starts at the outside brass part of the bulb in the socket, goes through the socket, onto a ground wire, and is usually bolted to the sheetmetal at the rear somewhere.

If you don't believe that it's a ground problem, get a long scrap piece of wire, strip one end and jamb the copper strands down beside the bulb, and hook the other end to the battery ground. If this fixes that side, it's a ground problem.

 

Excellant, thanks for the advice. It's freezing outside now so it'll have to wait till tomorrow but good stuff then. Both sides of the rear lights are grounded to the sheetmetal behind the lenses but I did NOT clean them up at all. I'll yank em off and clean them up really well and try it and your fix too. Thanks.

 

I started a new thread along the same lines but I wanted to update you on the wire from the side pod the bulb to the negative battery cable. By the way first I cleaned Al the grounds i could find. One on either side of the bed behind the lenses and tw but theno under the truck. One mid bed and one just in front of the rear bumper. I sanded them all to bare metal and replaced the two under the truck with 14 gauge wire. No real change but then I did the wire to the battery cable and still no luck getting the signals or the brake lights working with the headlights on but the stop tail and turn without the headlights on did get slightly brighter. I'm assuming that this is due to just a better quality ground.