Quoted from Doot77:
Ok so from what I can see the ball count unit is never energized until you’ve played thru 5 balls( 1 for each player and 2 for player 4).
Aha. That helps. Check this out:
CF ball count (resized).jpg
It looks like the Ball Count Step Up solenoid should fire when the Player Up Unit disc is on the last player and the Outhole relay fires. You say it works fine for a 1 player game. In that scenario, the pulse to the Ball Count Unit Step Up solenoid goes around the Player Up Unit disk, through the Gray-Red wire and through the Coin Unit Disk. For 2 and 3 players it misbehaves, which would require the pulse to go through the Player Up Disc and through the Coin Unit Disc.
The problem may be that the pulse is getting lost in either the Player Up Unit disc or the Coin Unit Disc. Since the Ball Count unit does eventually fire, it seems that the Player Up Unit disc is advancing and eventually connecting to the Ball Count Step Up solenoid by bypassing around the Coin Unit disc on the Orange-White wire. That makes me wonder about the Coin Unit disc (in red). It seems to work fine in the Player 1/reset position. But does it advance properly and make the connections for multiple players? If the wiper on that disc steps off the rivet for player 1 but never lands on the rivets for the other players, that could explain what you're seeing.
With the power off you should be able to put the Coin Unit disc in position for various numbers of players, then check for a very low resistance (not just continuity) between the Orange-White wire and the three wires on the opposite side (Gray-Red for 1 player, White-Brown for 2 players, and White-Yellow for 3 players).
Alternatively, you could start a 2 player game and put a jumper between the Orange-White wire and the White-Brown wire and see if that plays correctly.