On Beam is one I've had and it was dead when I got it. Download the schematic and let's get to fixing it!

https://www.ipdb.org/files/1715/Bally_1969_On_Beam_Schematic_Diagram_continuous.pdf

This thread is full of a lot of good on beam fun

https://pinside.com/pinball/forum/topic/to-me-or-not-to-me/page/5#post-913744

Looking at that schematic, there are three switches that should be adjusted normally closed. If any of those switches are open, none of the coin mechs will work.

Front door anti cheat. Front door kick. Coin bounce.
I'm not 100% sure where those switches are but I would bet they are near or on the coin door

You are right that the credit mech will hit a switch and open it at “0” and hit a different switch or set of switches at max. The max can sometimes be adjusted to different numbers by moving the post that hits the “max” switch

These are mechanical things and with a little time and study, you can probably figure out how it works and take it apart and clean and rebuild it.

Check out pinwiki for a lot of info you may use

Go to the stepper unit section on this page and scroll down to the Bally credit unit section to see pics of working units.

http://www.pinwiki.com/wiki/index.php?title=EM_Repair#Stepper_Units

Hope I didn’t confuse things. I looked at the schematic I found on ipdb. This is what I saw.

9A34D5AD-FA51-4EFF-B059-799DAD7BA8C8.jpeg