Chip, First, the two relays you pictured should actually be the KS (Advance Unit relay) and the FS (00-90 Unit relay). AS just designates the generic type of relay Gottlieb used (Second, the KS has one of the filthiest copper circuit boards I've ever seen in a working game.

You pretty much understand how the bonus unit advance circuit is supposed to work.

So when you manually rotate the spinner with a game enabled, does the C relay (Spin Target relay) energize?
The C relay should have 2 normally open switches on it. The closure of one of those switches (one switch terminal has a red & white wire going to it) should result in the coil for the KS relay stepper getting energized.

If the C relay pulls in, but the coil of the KS relay NEVER energizes, then the switch on the C relay should be checked for adjustment and cleaning. Also check the switch tab ends to make sure the solder connections are intact and a wire has not broken off. If the KS relay coil still does not energize, the coil itself may be discontinuous.

If the C relay never pulls in, then the switch on the spinner is not functioning OR the wiring between the spinner and the C relay is not continuous.

I cannot recall: is the KS relay located in the backbox? If so, then the wire comes to it through a Jones plug. Check the wires on the Jones plugs and try reseating them.

Lee

The copper traces on the KS relay circuit boards are filthy, but they have nothing to do with the KS relay coil not energizing. Need to solve that problem first and also "carefully" clean the copper on the circuit boards.

Good work. You were able to determine that the KS relay is actually "trying" to energize, but the mechanism isn't moving well. In that case, the filthy circuit boards and maintenance state of the relay are most likely the cause of the malfunction.

As others have suggested, clean and degunk the unit and see if you can get it stepping reliably.

If you really run into a brick wall, perhaps I could make a housecall and see if 2 heads are better than 1. We probably live about 20 min apart.