If I found the correct wiring diagram on bwinger’s site (and it is in color!), there is a white wire from each brake light switch that are spliced together in the harness. From that splice a single white wire runs through a 3(?) wire connector and on to the brake side of the tail/brake light.
Break out your DVOM, put it in ohm mode, and remove the brake lamp from its socket. With the brake switches off, place one of the meter probes on the white wire contact in the brake socket and the other meter probe to a good ground.
If the meter reads OL or infinity, the white wire is not shorted to ground.
In that case the bulb and/or socket might be shorted to ground.
If your meter shows some resistance, the white wire is grounded.
Move back up the white wire and repeat until you find where the white wire is shorted to ground.
You could also disconnect the white wire from the switches.
Then activate each switch. If the fuse blows, the switch is suspect.

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