I was driving my '47 Super 8 home the other day after getting the engine rebuilt, and I noticed at one point that my brake lights were not operating. This happened several years ago on a cruise and a friend replaced the brake light switch in the parking lot of the hotel -- easy. This time around I did it in my garage, using the spare I had bought after we got home from our vacation and this one failed also. Could this be another bad switch or is there a fuse somewhere that I don't know about? Also, the bleeder screws are absolutely welded shut and I've soaked them with PB Blaster to try and turn them to bleed the system, even thought I was careful not to introduce any air into the master cylinder while reinstalling the new switch and I do have brake pressure with no soft pedal. Am wondering if there is an unfortunate air bubble that is preventing the switch from activating, but I have never had this issue with any other car after a swap-out of this switch. Any ideas?

Could be another bad switch and they are relatively inexpensive if you want to get another to try. If you have silicone brake fluid that seems to shorten life of the brake switches.

If wiring is stock, the brake lights are powered from the constant power at the headlight switch and protected by one of the two auxiliary fuses mounted on the headlight switch assy. The same fuse can also power other things so if nothing else appears to have failed it may not be the fuse.

As you apply pressure to the system via the master cylinder piston, the developed pressure is equal throughout the system including on the brake light switch. Thus, even if a tiny air bubble happened to lodge there, it would not prevent a functioning switch from functioning as long as the triggering hydraulic pressure was reached.

Agree with HH56. I have seen many switches go bad with silicone brake fluid.

I have not heard that before. I stay away from the silicone because of an extremely bad experience many years ago, and only use Dot-3 or Dot-4 in every car since.

Quote:

?? DOT-5 is silicon based... DOT-3, DOT-4 are not. DOT-5 is incompatible with 3 or 4.

To the best of my knowledge DOT-4 synthetic brake fluid is not silicone-based. Synthetic and silicone-based brake fluids are based on different chemistries.

https://en.m.wikipedia.org/wiki/Brake_fluid#DOT_4