Weary of testing switch inputs on your WPC machine? Not sure if the issue is your MPU board or the machine wiring? This test board plugs directly into the MPU connectors, and has all 72 switches on it. 64 are standard matrix, and 8 are dedicated switches (which is where the switches are for test access). Each matrix switch also has a 2 pin header next to it that allows you to put a jumper at that location.. for instance, many times opto inputs are normally closed. Note that there is a jumper already fitted on the column 2 row 4 location, as Williams placed a diode there to verify that it was connected to the game. Without it, you get an error message. The board comes with the 3 jumper connectors and shunt jumpers. It comes with a 60 day warranty against defect.