5 volt power supply for logic, and two main logic boards, a relay board and logic board, these baby's are expensive. The relay board has the field wiring terminals and can be found on the prints. It comes down to your control voltage, P24, being pulled to ground with the logic board to initiate a circuit. If you can get a manual, they have pin identification for signals on the chips and drivers. and a manual has a set of prints in it hopefully.