The schematics You show in post-1 has on the right hand side a switch drawn closed named "Game-Over-Relay" - it is a switch on the "Powerside-Connection" --- in post-7 You write "Bonus-Relay locks-on when the pin is powered-up" --- does this means AAA: When You toggle-on the main power switch ? - or BBB: After toggling on when You then press the left flipper-button ? - or CCC: When You then press the Replay-Button ?
When the Game-Over-Relay trips at a time: The pin changes from "in play" to "in Game Over".
When the Game-Over-Relay latches at a time: The pin changes from "Game Over" to "in play".
I made me a mnemonic help: The word LATCH consists of 5 letters - the word TRIP consists of 4 letters --- four is "5 less one" --- the latch coil armature has one nylon ladder mounted - "one less one" is zero --- therefore (mnemonic aid): The trip armature has zero nylon ladders mounted.
Test-DDD - please toggle-off the pin - look in the cabinet for the Game-Over-Relay with two coils mounted on the relay. Do "latch" the Game-Over-Relay (means You press the armature having the nylon ladder mounted) --- then toggle-on - nothing shall happen. Then You press the left flipper button and You MUST see the Game-Over-Relay TRIP (((At the same time: The Lock-Relay pulls-in and stays pulling))).
Please do Test-DDD --- IF (if, if) the Game-Over-Relay does NOT trip: Toggle-off the pin - manually TRIP the Game-Over-Relay --- then toggle-on and press the left flipper-button --- what is the Bonus-Relay doing ?
When we are nice and friendly to the pin: We play through all the players / all the balls - at end of every ball the bonus-ladder is counted down to Zero - therefore the bonus-ladder (also) is counted down at end of the last ball just before reaching Game-Over.
Please be helpful (toggle-off the pin) - manually step-down the bonus-ladder - step it down to Zero-Position. This makes a switch to open - the switch in post-1, JPG, left hand side : "Bonus Unit open at Zero Position". Then toggle-on, press the left flipper button, start a game - WHAT is the Bonus-Relay doing ? Greetings Rolf