See the relay in the middle, this just switches a possible ground path on/off, and is the transistor controlled item in the circuit. The flipper button completes the circuit, providing the ground. Yes, the full voltage will run through the flipper switches, until fliptronics/electronic flippers all pinball machine flippers operate this way (full power through the cabinet switch). This is why those switches are always the big fat tungsten contacts and why they spark occasionally, even well into the solid state era.
What happens with the cabinet switches is when you file the contacts which you have to do occasionally, the dust from that lands on the switch body and provides an alternate path to complete the circuit. Removing J2 from the solenoid driver board will take the cabinet switches out of the circuit, so if he does that and the flippers drop/don't go up, the problem is in the cabinet.
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