score motor cam switch 2A stuck closed?

if not, is switch 4A stuck closed?

if not, is the outhole relay powering when you cause a left bonus advance?

ugh.

well, the outhole relay shouldn't power unless a ball is in the outhole and the bonus unit selected by the alternator relay is zero.

is your outhole switch gapped really small - if you knock on the playfield near the outhole, does the outhole relay power?

a flaky score motor 5D switch could cause extra pulses to be generated to the bonus and replay units, but that wouldn't explain the outhole relay powering when you hit the left advance sling and causing the ball release to fire.

post #3 says the outhole relay is powering.

'course, maybe there's some confusion between the outhole relay vs. the ball release solenoid. The solenoid is the thing that kicks the ball over to the shooter, while the relay is on the bottom board.

assuming the outhole relay is powering, there's no obvious switch/wiper that could be causing it ... so that leaves a short somewhere.

if the outhole relay is powering and the score motor is doing a cycle (an outhole relay switch will cycle the score motor if nothing else does), then 4A switch will cause the release solenoid to fire ... assuming the outhole relay was powered before 4A pulsed closed. I read post #3 as the solenoid firing is just a side effect of the outhole relay powering.

I think the OP couldn't see a sensible solution on the schem because there doesn't appear to be one. If the left bonus unit is close to the outhole or outhole relay, and a switch is gapped really small, the vibration of the step-up coil could cause a switch closure and the hold switch will keep the outhole relay powered.

"hit it with a hammer" is a valid debug approach

otherwise, seems like there needs to be a short.