The playfield plugs into the head? I thought it plugged into the bottom mech board, and that plugged into the head. Memory may be failing...

Are you troubleshooting a stuck/buzzing score reel?

Is the 100 point relay on the playfield or mech board? You might want to check score motor switch 2C and the the 500 point relay switch with the green/red wire and blue wire...

removing all the playfield plastics makes finding a closed switch easier.

Hi Allen
I do not like meters to measure "continuity" I have one - but I seldom use it. The problem in an EM-Pin is: Therea are many wires and You can measure "continuity" BUT there is NO continuity - you may have a loooong connection all the way around through the (wires in the) transformer. To be 100% sure when measuring: You should (must) unsolder one side of "what You want to check for continuity" - and as I am lazy - I do not want to unsolder -> I do not use my meter.

Your description is not clear - did the pin run - and all of a sudden you have the strange problems ? OR DID YOU BUY A NON-RUNNING PIN ?

You have a "stuck 100-point-Relay (and therefore stuck chime)" - what about the 100-point-Score-Reel ? (Player-1)?

At what moment does the 100-point-Relay start "faulty-pulling" ?
The Main Power-Cord is unplugged - Relay is not pulling.
You plug-in the Main Power-cord - Relay ?
You toggle the main power switch - Relay ?
You push the "Credit-Button / Replay-Button" -> the pin starts-up - Relay ? -> the pin does the Reset - Relay ? -> the pin kicks the ball to the shooter-alley - Relay ?

I believe You have more than one problem - You mention: The pin then advances through the balls to "Game Over". This problem is usually not caused by a stuck 100-point-Relay - but lets see.

Please write about the 100-point-Relay "start-pulling".
One reason the pin can advance through the balls - After the Reset is done: The "Ball-Index-Relay" is faulty-pulling - or a switch on that relay is faulty-ALWAYS-closed.
Look at the Ball-Index-Relay - does it pull after Reset of the score-Reels is done ?
It well can be: The pulling 100-point-Relay does activate the chime AND does activate the Ball-Index-Relay.
When resetting and after reset: The Ball-Index-Relay MUST be "NON-Pulling".

Maybe we are lucky - You have a "faulty-always-closed (Self-Hold) Switch on the 100-point-Relay". Look at this relay - a short wire runs from one side of the coil to a switch mounted (on the relay) - have a look at this switch -> is this witch SECURELY OPEN when the relay is not pulling ?
Greetings Rolf