The signal box has optical sensors built-in and has a sensitivity adjustment. Just apply power and put them next to the track. These sensors will do the rest. They have separate inputs and outputs so they can be daisy chained. They have two outputs, which are complimentary, so they can directly operate other signals using LEDs like the MTH 3-light cantilever signal. Signals using lamps or solenoids will require our DZ-1008 Relay Module. The MTH 7-light (Pennsy style) signal also requires a relay or the new DZ-1075.