I recently got my first EM pinball machine and it is a different world from what I am used too! The machine is a 1975 Williams Pat Hand. I have been tinkering and it goes through most of the start up sequence but after the bonus unit resets to zero the bonus unit just keeps cycling as does the bonus relay and the score motor keeps running. If I take the ball out of the trough, everything stops but with ball in the trough, the outhole relay never comes on and the ball release coil never fires, nor can I get it to start a game. I do have the manual and schematic but it is not like reading a wiring diagram and I am confused as to where to go next. Any help would be greatly appreciated!

Thanks for the reply! I did check the zero position switches on the bonus unit, there are 2 of them. One opens when the bonus unit goes down to zero and seems to work fine and the other opens when the second coil on the bonus unit fires(I guess the one that steps the unit up one from zero) and that switch seems to open fine as well Both switches look to be normally closed and do have continuity when closed. There are only 2 wires to each switch so neither looks to have a normally open position. I will check out the score reel switches when I am home later and can post a pic or video of the bonus unit cycling. Thanks again.

Here are a few pics of the bonus unit. The top coil fires, opens the zero position switch with the little arm in the center, then the coil on the right side fires and steps it up one. As soon as that happens, the top coil fires again and the cycle repeats as the score motor runs. This appears to be the last step in the typical Williams start up sequence but it never fires the ball release or starts a game. And the outhole relay never moves. It looks like someone had resoldered a whole bunch of the wires on the score motor so I did double check to make sure the right color wires are at the right position and that all switches operate and conduct when closed. Once again, I am no t that great with figuring out where to go in the schematics. if a zero position switch on the score reels was not working, wouldn't the reel keep running?IMG_4136.JPGIMG_4140.JPG