[dmjlambert]

The spring loaded disc outer edge sits on the plastic of the steering wheel and that spring disc is in constant contact with the pin on the canceller, and the cup that holds the button. So the whole assembly is connected to the relay negative terminal. When any part of the button or cup is pressed, the spring loaded disc inner hole edge snaps down and makes contact with the metal raised portion of the inner steering wheel hub near the steering wheel nut, and that connects it to ground. That is what activates the relay.