Probably won't get a chance until the weekend now to completely follow all your testing, Dave. Tonight I was able to quickly test the Reset Relay and it didn't seem to be the switch I suspected.

What I did discover was that when I reset the Coin Unit, Player 2 was lit on the backglass. I turned the machine off and manually put the Coin Unit on Player 1. Looking at it, it is REALLY bending the switch down on the Coin Unit. I turned the machine back on and pressed start. It buzzed differently to before and went through the reset sequence and kicked the ball out. The flippers also worked. When I turned the machine off again and pressed start a second time, the machine seemed to lose power if it wasn't initially on Player 1.

The Coin Unit doesn't reset freely and will need to be pulled apart and cleaned properly. Is the power issue switch related or wiper related? Out of interest, what can you use to clean those wiper contacts?