This happens all the time when people do tail eliminator kits. A little search on the forums will give more insight. My guess is the wire to the actual brake light was pinched and the vibrations finally caused it to cut and short. You probably blew a fuse as well.
As said above, trace it out. Look for loose connections and cut wires. Who knows, you may have just had the filament in the bulb drop. You could check it and make sure the 2 wires in it are in good shape.
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