Help, please. Electrical Problem

[Lon66ChevC10]

Here's the situation. Tuesday night at I put my foot on the brake and the dash lights dimmed on my 1966 Chevrolet C-10. The second time I put my foot on the brake, the dash lights AND tail lights and brake lights all went out completely.
Wednesday morning I replaced the fuse (which was blown) and the dash lights, brake lights, and tail lightsseemed to work okay. However, that night I had the same problem. Dome light won't come on either. But if I shut the truck down, let her sit for a while, then start her back up- all the lights come back normal--- UNTIL the I put my foot on the brake again. The fuse has popped a second time so I obviously have a short somewhere.
My question- how exactly do I check for a short? I traced the wires from the tail lights all the way up to where they go through the firewall into the cab and everything seems okay on that end. I've just barely started tracing wires inside the cab.
It just seems weird that the problem "resets" itself after shutting the truck down.
If anyone can offer any advice I would sure appreciate it.
Thanks!

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1966 Chevrolet C-10 pickup 4-speed manual with a 1975 250 inline 6