I had to check my pinpot to confirm how the switches are wired. They are independent of each other, thus it can’t be a single switch, resistor or cap IMO.
In reading clay’s description, the PIA pulls the 7408 low to operate the coils in test mode. That works. The PF switches also pull the 7408 low on other inputs for this IC, which then go to the 7402 and pre-driver and driver transistors (tip122s). Clay states though that if the either trigger (pia or PF switch) operates the coils, everything from the 7402 and after (pre driver and driver) must be ok, however I question the 7402 myself.
The reason is that I find it hard to believe that all PIA inputs for the 7408 would be fine, but all inputs for the same chip would be shorted for the PF switches, as none work in game mode. I would test the 7402 on diode settings against another 7402 known to be good.
We do know that the driver’s and pre driver work, and the PIA must be fine, so it likely lies within the 7402 and possibly the 7408. I would test them myself, but they are dirt cheap and replacing both should cost $1, and be easy enough to do.
Hope that helps, maybe someone else can chime in.