If the blue/white wire color goes too many places, you can narrow it down by checking the colors on the Ball Release coil. One side (black) won't be interesting, but the other side of the coil should be a distinctive color. Once you know that you have identified the Ball Release coil, you can find it in the game and actuate it by hand (with the power off) and look for a switch that is detecting whether the plunger is pulled in.
.................David Marston

Without seeing the whole schematic, I have a theory: maybe the circuitry we are discussing that energizes the O coil is far enough up in the schematic that it's beyond a game-over switch that should be disabling the scoring and the like. In other words, O should be a step along the game over sequence that is followed by some other relay activation that will turn off the whole zone of the wiring where the O coil is getting power.
1. What does the relay chart say about O? Name of relay? How many A, B, C type switches?
2. What cut-offs are below the zone of the relay where the O coil is found? (Please include the name of each relay.)
3. Can you locate every one of the switches on relay O somewhere on the schematic? The most interesting ones might be involved in activating an XB or QB lock-in relay.
.................David Marston

Yes, the 1A in series with some other motor switch is there to shorten the pulse. So that's how O would get shut off.

If that switch on XB isn't opening as it should, there are lots of things that stay energized, so you have lots of ways to test whether that right-side rail has power.
.................David Marston