Finishing up my Mystic PF swap, think, hmm, that's odd, certain lamps locked on at on U1 on lamp driver board (didn't surprise me because the original game had many bad sockets, so thought was old problem). Put another Lamp driver in, problem goes away, figure, it's U1, right? Replace U1 on original board, same issue. Also seemingly unrelated, switch column 4 is not active but I figured that was something else.

Measured between GI and controlled lamp feed voltage showed that the switch column strobe was always high.... hmmm.... u1 enable and strobe= same signal on PIA.

Turns out 2 sharp wire ends on both a GI bulb AND a controlled lamp were piercing the column wire at 2 different places. Snipped and rerouted, all fine now. The clue that there was 2 cross connects was that the controlled lamp wiring stopped showing continuity to the switch column after I moved the harness, but the GI STILL showed. I thought the GI and the controlled were just cross connected somewhere else.

Real PITA though.