Would be nice if you said what your problem was. Does the brake light stay on all the time or does it never come on?
One wire going to the switch is hot with the ignition on, the other becomes hot when switch is activated and feeds the rear brake light. If the light is staying on all the time, disconnect one of the wires on the switch. If that fixes it, the switch is bad. If it doesn't, then the problem is somewhere else. If the light doesn't come on, then use a test light to see if you got voltage at the switch. If you do, pull both wires off the switch, touch them together, the brake light should come on. If it does, the switch is bad.
Retired Navy, MCPO