Motorcycle tail light works, brake light does not?
bad bulb ,or the fuse is blown,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,
Change the bulb. Tail light has nothing to do with the brake light.
Most likely the bulb is burnt out. Or 1 filiment of a 2 filiment bulb is burnt out. Less likely , a fuse has blown or a wire has come off. Even less likely, but possible, the brake switch has gone bad.