Sunday, June 25, 2023
An unexpected problem has cropped up with the Plymouth. After regaining brakes (by refilling the master cylinder — duh!), I find that my brake lights do not work.
I bought a new brake light switch (its a hydraulic switch, not mechanical) along with the new master cylinder. I don’t have a socket that fits the switch (yet), and I’m hesitant to use a pipe wrench on the thing.
I’ve tested the switch — had my son hit the brakes while checking for the switch to close — and nothing happened. Then I checked the wiring.
One of the wires from the switch routes 12 vdc to light the tail lights when the brake light switch closes. The other wire on the switch SHOULD provide 12VDC so the lights can light when you hit the brake.
No voltage on that wire; well, there is something on the order of 5 volts on it, but no light action at the rear.
I jumped 12VDC to the wiring to the tail lights and they work just fine. Its the damn switch and/or the DC voltage that’s either not working or missing.
I’m not sure how both fucked up at the same time.
Today I wanted to trace that 12v line back through the firewall, but it gets wrapped up in a major wiring harness under the hood before I goes through the firewall.
Right now, the easiest solution will be to run a 12v fused line from the starter relay to the brake light switch. Per the wiring diagram, the 12v is provided originally from the headlight switch. Why its not working, I don’t know yet.
While poking around under the hood, I also found what looked like an overheated piece of wire. It looks like it had been shorted to the ground,, the insulation was partly melted. It wasn’t a wire in the original wiring harness. Not sure yet what the hell that was supposed to do.
The diagram does list the wire colors, so it may be possible to trace the wire — or at least locate it’s connection to the headlight switch. There’s supposed to be a bi-metallic circuit breaker on the switch, so there could be an issue there.
More investigating to come.