Start by looking at the Ball Count unit and Player Control units. Do they try to work, and do they work when you activate them manually?

Pinball (resized).png

Pinball (resized).png

I'd try to troubleshoot the issue with the ball count unit by starting a 1-player game first. You'll need to check the circuit that sends power to the ball count step up coil (solenoid). Check the following:

Out hole relay switch - green wire and grey/yellow wire
Ball Index relay switch - grey/yellow wire and yellow/red wire
Extra ball relay switch - yellow/red wire and red/yellow wire
Score motor switch A-4 - red/yellow wire and green/orange wire
Coin unit wiper switch position 1 - green/orange wire
Circuit fuse - black/blue wire

Check these switches to make sure they are clean and adjusted properly. Coin unit wiper switch should be centered on the position 1 switch. Check the circuit fuse to make sure it is fully seated in the fuse block; check to see if the fuse is good...