I've been playing around with this for a while, disconnecting switches and even trying another WPC-S board to try and find the problem and I could use a little help pointing in the right direction. The left phurba control switch is triggering the following switches:

coin door closed, 22, wht-red grn-red
buy-in button, 23 wht-orn grn-red
m(o)ngol target,26 wht-blu grn-red
mongo(l) target, 27 wht-vio grn-red
mong(o)l target,28 wht-gry grn-red
L. Phurba, 34 wht-yel grn-orn
trough 4, 44 wht-yel grn-yel

So it triggers the left phurba like it should, but also all the others listed. It triggers a bunch of grn-reds even though it is green orange. I have disconnected all switches listed and it persists. I also hooked the harness for the left phurba button to the right to verify it is not the left switch or diode. Disconnecting J207 corrects the issue, so it is likely something hooked up to that connector (?), but I have no clue what. No other switches appear to be an issue. Everything looks good under the playfield, unless I missed something.

Any idea where to look? Does the switch list give a clue? I'd rather not test every diode on every switch, not sure if it is even a diode problem.

Any help is greatly appreciated! Thanks in advance!

Bump! Thank you very much, but I am still stuck on this. I've disconnected all switches that show up (and more) and it still is doing it. In all my years this is the only thing I haven't figured out. If anyone has any other ideas please let me know! Thank you!