I suggest breaking down the problem. With just the MTH ITAD hooked up, can you hear the relay click "on" (you may have to put your ear near the ITAD in a noisy train room) when you wave your hand or roll a car in front of the sensor window? Does it then click "OFF" after some adjustable (delay knob) delay? Can you also see some effect of turning the Sensitivity knob? When turned to higher Sensitivity, it should detect your waving hand or a passing car/engine at a longer distance from the window.