Hi Raikus
I look at the schema in ipdb.org. The switches for the "Coil on Outhole-Relay" (and the coil) are 14-C / -D / -E. It is a bit complicated: Bonus-Ladder must be stepped down to Zero, then up one step and the Ball-Release-Coil must fire and the ball must leave the Outhole (so opening the Outhole-Switch).
You write "Checked Bonus-Unit Switches, Bonus (Count) Relay, Outhole (Kicker) Relay".

Did you check the "Switch depressed by the Ball laying in the Outhole (between the Flippers)" ?

The Outhole-Relay has a "Self-Hold-Switch" (schema-C-14). At some time (shortly after kicking the Ball over to the "Shooter Lane"): The Outhole-Relay shall loose its "Self-Hold-Current-Circuitry" (and therefore let go). A bit below and a bit to the left (in the schema) there is a line / wire and an arrow "to R-BR at C-3".
So I look at schema-C-3 and see: The wire R-BR has (to the left) a connection with "Score-Motor-fifth-Wheel-Switch-B (a Make and Brake-Switch) - HERE MUST OPEN so the "Self-Hold-Circuitry of Outhole-Relay will be cut".

Did You check Score-Motor-5B ?

Greetings Rolf

When the game over relay trips, are there any points scored on player one? If so, then my best guess and most likely the problem is that you have a stuck playfield switch.

Is this a game that you just picked up or have you had it for awhile? Check the switches in the coin door. They can cause weird things to happen if they are not gapped properly.

I'm with Rolf on this one. The schematics are posted on IPDB. Haven't studied Williams schemas, but they are all somewhat similar. Looks like 5B is the most obvious culprit, but I would also check 'Index - D'.

Another question, Have you manually moved the score reels to check that they reset to 0?

Hi Raikus
If SCM-5B opens correctly - If the "Self-Hold-Switch on Outhole-Relay" would be "faulty always closed (bent blades)": The Outhole-Relay would "flatter" (on -> off -> on -> off ...) because SCM-5B opens correctly (Outhole-Relay goes off) -> Score-Motor keeps on turning (wants to get to the end of its 180 degree-turn) - so SCM-5B closes again -> through the "faulty always closed Self-Hold-Switch on Outhole-Relay": current can flow -> Outhole-Relay goes "on" again. So look if the Outhole-Relay "flatters".

I am trying to avoid "digging into the logic of stepping down the Bonus Unit to Zero - then step up one step - and (by the way, by the way) kicking the ball over to the Shooter Lane" ...
You write (post-5): a friends pin - having a big party -> (question ?) NO REPLAYS ON THE COUNTER / NO COINS AT HAND TO THROW IN -> opening the Cash-Door and fumbling on the "Coin-Switch" (?)
Read here: http://www.pinrepair.com/em/index2.htm -> 2c. Before turning ... -> look at the first picture and -> read text after picture-3 -> "beeing romantic" ...

And in the schema at C-3 / C-4 there are ALL switches shown, the switches for to let the Score-Motor run. And at C-2 I see: Wire-yellow -> upwards through closed "Anti-Cheat Switch" upwards to "25 Cent-Switch (a Make and Brake Switch) -> to the right -> wire-Green-Orange -> through a "Switch on 25-Cent-RELAY" -> wire-Orange-Green -> ALSO feeding electricity to let the Score-Motor run.

If (if) your friends have fumbled at the Coin-Door-Switches and have bent blades on that delicate "25 Cent switch": 25-Cent-Relay might be pulling endlessly and through the switch on (pulling) 25-Cent-Relay -> Score-Motor runs. So this is the "background story" to Hi-Fi's tip. Greetings Rolf