The 12v DC controlled output from the controller is passed through the unit. Connection between unit, power source, controller and track is achieved via six terminal connections. The unit superimposes a harmless high-frequency signal over the output from the controller. When a poor contact between locomotive and rail is detected, the unit switches on, ionising the gap and burning off the dirt, switching off again when contact is restored. Compatible with GMC-SS1 and GMC-SS2. (For A Single Track).