Quoted from Quench:Grounding the metal end tabs of those lamps you're pointing to shouldn't have caused any issues.
Is there any possibility your ground wire accidentally touched one of those three bare twisted wire connectors coming off the flipper switch stack? I'd suggest wrapping those twists in electrical tape for now or deal with them properly by soldering and heatshrink insulating them.
The MPU board has very little/barely any battery corrosion so you're lucky in that respect.
It's a pity someone has soldered in the battery backed 5101 RAM chip at U8. Makes it harder for you to put a NVRAM chip down the track.
Anyway, with the machine off, carefully pull out the 6810 RAM chip at U7 and reinstall it and see what happens.
Note your CPU at U9 is an AMI brand chip and they have a higher than normal failure rate.
Was thinking the same about that switch stack. Man, that's ugly and just screaming "I'm gonna cause you trouble...I'm right here waiting!"
Also, if he has a desolder gun and a socket, it shouldn't be an issue to get the chip at U8 out and solder in a new socket.