Gary,
It may be just the bulb. The signal and brake lights are on the same filament. If the bulb is good, check the wiring to the socket that's
not red - It'll either be white or green. If that has power, you may have to fiddle with the socket contact plate. If it has power, go under the dash and check the wires on the "Trailer" side of the relay (the side with 2 wires). If the appropriate one is dead, the relay may have died. By the way, it's more reliable to test by pressing the brake pedal, not by using the signal light.
