The brake lights stopped working altogether on my 56 Fury so some years ago, so I installed a new brake light switch and all is well. I use DOT 5 brake fluid, so suspect that is why the old switch may have quite on me. It may have been used to the old style fluid.
The only thing I can think of is to keep trying brake light switches until you find one that works. Remember, most of these switches are becoming museum pieces. I have given some thought about the master cylinder, and there is nothing I can think of that would prevent a brake light switch from working other than a bad switch.
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