Dan,
Not sure of this but I think there should be an electrical switch that is tied to the movement of the brake pedal. You could see if it is adjusted properly and being triggered with the brake pedal. You could also activate it with the brake pedal and use an ohm meter to see if it changes state (high ohms to low ohms or visa versa) with movement. If not working that is something you could be able to service yourself.
Later Ed