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 to connect to your MPU and 10 shunt jumpers. It comes with a 60 day warranty against defect.
When you go to www.pinballreplacementparts.com, it is on page 5. Or it may be available here on Pinside.

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It can be used in gameplay, but you must be careful to jumper only the switches that should be.. like optos and the ghost switch. And yes, there will be other test boards. Most are designed to assemble a bench test rig though.

That's a cool idea, but would be a lot of work.. and you would have to convince me that there are more than 3 people that would buy it. And it would not work for Bally.. the signals are highly multiplexed, and you cannot sort out switch signals from other signals.. it is not all pure and clean in there.