When the score resets are clicking, what are the score reels doing? Do they run up to 0 and then keep going again to higher numbers?

If not, what happens if you manually set all score reels to zero and then try to start a game?

Schematic is from IPDB. Strange trying to download the schematic. Had to download it, nothing showed up, then opened it from my download folder. I now notice it doesn't open from the post I made on your Pinside thread, so try what I did and you may get it. When I open from my download folder I can increase it to original size crisp and clear.

xsvtoys did a thorough write-up of your machine's operation. It's a bit of a read, but it's well-done and you might find it helpful.

https://pinside.com/pinball/forum/topic/em-pinball-machine-complete-circuit-description-2-bally-monte-carlo#post-5180735

Is there a label that tells what that stepper is? It looks kind of like the 00-90 (i.e. match) unit, but that stepper should have a B-27-1300 coil.

one way to ID the thing is look at the wire colors on the coil. If black and white-orange, then it's the 00-90 unit. If you can't tell, sometimes you have to dig back into the harness to see the colors reasonably well.

if that fails, guess and use an ohmeter to check for almost zero ohms to something the schem says connects to the coil. Don't use continuity/buzzer since that may work thru the coil to other places - or disconnect the wire.

since it's a continuous stepper unit - no reset coil - that also eliminates the ball count unit and player up unit as possibilities.

the most likely thing is the 10 point relay switch in the circuit is stuck closed (or the 10 point relay is stuck on due to a playfield switch stuck closed).

using the B-26-1100 coil instead of the B-27-1300 won't matter. The B-26 may get a little hotter, but it'll work. You can change to the correct coil if/when you feel like it.

Right, as baldtwit said that is the 00-90 unit also called the match unit. It has the black and white-orange wires connected to it. That coil is energized and advances the unit one step every time a 10 point score occurs. Check the 10 point relay to make sure it isn’t energized when it shouldn’t be. The primary suspect is the switch on that 10 point relay that controls the 00-90 unit. It will have the white-orange wire on it. Make sure it is open when the 10 point relay is in its normal resting position. If it is touching closed it will then keep voltage on that solenoid.

Glad you got it working. I think it’s a pretty fun machine for an EM, there is lots to shoot at and it’s not too easy to get high scores. It’s also awesome to just look at with Christensen’s artwork.