My brake lights arent't working on my '57 F100. My turn signal switch was bad and I thought replacing it might fix the brake lights as they're on the same circuit. The new turn signal switch fixed the turn signals, but still no brake lights. All the lights work. Turn signals work. I've run a bypass wire on the brake light switch, and still no brake lights. There's power going into the switch, and there's power coming out of the switch when the brake pedal is pressed, but no lights. My thoughts are it has to be something downstream from the switch. Before I start cutting into splices, I was hoping someone had the same issue and figured out a fix. I've seen some threads about brake lights not working with a pressure switch, but nothing seems to have any resolution.
Grounds..... You may have to run some from the lights. Frame....bed wood mounts....rust....paint....those lights need all the help they can get.
Okay, since your turn signals work, you know the bulbs and the wiring to the bulbs is good. The brake light switch should be feeding the brake light current to the turn signal switch. You need to trace the wire from the brake light switch to where it connects to the turn signal switch. I don't have a 57 F100 manual, but Ford used the same color code on wires forever. I checked a 56 Mercury manual and a 57 Ford T-Bird manual for color codes and they were both the same. The wire from the brake light switch to the turn signal switch should be a green wire. You need to find out if you are getting power to this wire at the turn signal switch when you step on the brakes. If you don't have battery voltage there, the brake lights won't work.
That's a long run of wiring all the way back to the tail, lots of SAE connectors along the way, not counting any hinky "splices" along the way. Any electrical connection will fail, eventually, due to roadspray, salt, and corrosion. Try to soak them in solvent before pulling them apart. Also beware mice chewing on the wires. Those big block pin connectors through the firewall are a really handy spot to divide the wiring harness in half. One of those Ice Pick style test lights work really slick for this testing. Start there, and you'll probably find that everything works fine, but as you work back towards the tail, shit starts getting wonky or fading out. Also those brake light switches can test OK for continuity but still be Inop. Seems to me they might even pass with a test light right at the pins, but they won't actually light up at the tail itself. Hope this helps! Something so "simple" can really start to piss a feller off.
JaRacer gave you the exact instructions to follow in post 3. Your issue is between the stop light switch and the turn signal switch. If the lights flash with the turn signal the wiring from the signal switch, bulbs and grounds are good. You are not getting power from the brake light switch to the turn signal switch. The end solution is probably going to be what Goldmountain suggested in post 5 in that you will have to replace the wire between the stoplight switch and the pigtail on the turn signal switch.
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