Put your multimeter on continuity test. You see the green wires screwed down to the case of the isolation transformer? Put one side of your meter there, and the other on the brown wire at the plug you are trying to identify. It should be the same wire/ If it is, that is Earth Ground.
Thanks, I had tried that as well with all three of the purple/blue/brown connectors, and none show continuity. All three of them show continuity to the AC connectors on the switcher power supply though, but none show any to ground. It's almost like all three are supplying ac and there is no ground, does that make any sense?
To add to the mystery, I was googling all over for images of the inside of Time Pilot cabinets and found a video on John's Arcade Youtube channel where he restores his, and at one point he shows the inside. It isn't quite clear enough to be sure, but the monitor power connector that plugs into that cabinet monitor power connector seems like it has only two wires attached even though the connector has 3 holes. It's almost like only two are being used to feed ac to the monitor and there is no ground. I thought you had to send ground back from the monitor to the isolation transformer no? Anyways it's not completely clear so I can't be sure.
EDIT: This is the exact time he shows the inside of the Time Pilot cabinet for a little bit:
https://youtu.be/AzcQtwYH3bs?list=PLF6Omn2cXb7aoTe310XPwV3qt-yE9CMIm&t=342
And here very briefly is a closeup of the power connector, but he pans so it's blurry:
https://youtu.be/AzcQtwYH3bs?list=PLF6Omn2cXb7aoTe310XPwV3qt-yE9CMIm&t=388
If anyone has a Time Pilot cabinet, or possibly any Centuri cabinet, can you check if only two of the three pins are used on that cabinet monitor power connector?
So, if you have a black and white wire on your monitor, they can go to either one of the purple and blue wires. The ground is the important one, it should go to the monitor frame.
That's what I thought, so I was like ok let's find ground. Figured brown traces back to green on the isolation transformer so it would be ground. But none of them test continuity for ground, and all seem to test continuity to ac, hence I'm confused lol. My only thought at this point is that all three are ac, there is no ground on it, and the monitor power connectors only use 2 of the 3 pins (black/white). But would need a picture of someone else's cabinet on the inside to be sure.