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On my 79 F250 I recently lost brake lights first. I didn't do anything with it since I tore it all apart again to switch flatbed setups. I had a new switch therevso I put it in while putting everything back together but still no brake lights.
So what I've figured out is I only have power to the brown wire for parking lights. I tested the others except backup lights and no power at the rear. Is it possible part of the headlight switch went bad or turn signal switch?
Wiring is not my thing, I get through it but I don't enjoy it.
If the brake pedal switch is good and has power to it and coming out when depressed then you start tracing from there to rear brake lights to see were power loss is at
I shoulda checked it before I left for lunch at the pedal but I didnt. I had put a new switch in this morning figuring that was the culprit. So no power at the rear with old or new switch but can't say at the lead to the switch. Not having power to the signals seems like it's more than just a brake light switch.
Yea wiring sucks when troubleshooting,,since your signals are not working it could be turn signal switch as possibility , I would check and make sure of proper bulbs and that the sockets are grounded good might be worth checking the flasher relays and the plug at steering column , some wiring diagrams are here 1973-1979 Ford Truck Wiring Diagrams & Schematics - FORDification.net
My lights aren't factory and they are new. The grounds are really good since I just had to move the lights and grounds again since I made a dump bed. I'm going to have to dig deeper with the wiring diagram I'm afraid. I wanted to check ahead of the brake switch tonight but didn't get to it. Finally got my bed in the air tonight on its own.
Where are the light mounted, to the bed?
If so you may need to run a ground wire from each light to the trucks frame not the dump frame.
The brake light switch should have power all the time to 1 side and only power when pedal is pushed.
The power out of the brake switch to the turn signal switch where it is sent based on if a signal is on or not to the rear. Another set of wires goes to the front turn lights.
Now you say you don't ANY lights out back? If so could be the ground as said above or the wiring to the rear is bad somewhere up front.
I don't know if your truck has a plug up front to the rear harness like my 81 F100 does? Mine is at the frame rail/floor board below the master/booster assy.
If so that could be a bad connection and why no lights outback.
Time to break out the test light and stat checking for power on that rear harness.
Dave ----
Lights are mounted to the frame, brackets are clean of paint so is frame where the brackets sit against. Each light also has its own ground to the frame. This setup has worked flawless last year or so. I do have parking light power just nothing else. I do also solder everything, I do not use any crimp connectors.
I hope to check it out more yet this weekend just didn't have time yet.
Also went at the rear with test light the other day when I started this thread.
Update-
Tonight I had some time to investigate and shoulda before I asked for any help. Turns out I had a big mess for some reason besides wrong size fuses.
2 bad tail light bulbs
1 bad reverse
1 messed up signal flasher
B/U fuse blown
Turn signal Fuse blown
Emergency Fuse blown
Bad new brake light switch...put the old one back in
The Fuses probably woulda blown anyway but they were all 7.5A where they shoulda been I believe 15 or 20....that part wasn't me. We'll see how long it lasts but I have a feeling my regulator might be messing up again. I had to change it before when it was making like 17v at idle.
If that's the case I'd like to try one of those soft start relays I read about. It seems no matter what I do my alt will squeal the belt like crazy on startup usually till rev it up once. New belt, proper tension nor belt dressing ever helps it.
