P1 switched lamp bus. Goes to anode of opto isolater triac driver MOC3011-U1
P2 Lamp SCR Connection. Goes to cathode of opto.
P3 GND
P9 +43v for relay and selected bank of solenoids
P4 Jumper brings +43v here when expander board used to do banks of solenoids. Probably NC on the harness.
P7 When relay on, this pin high impedance. When relay off, This pin is +43v (2nd bank of solenoid's hot side)
P5 When relay on, this pin goes to 43v. When relay off high impedance (1st bank of solenoid's hot side)
The relay is turned on when the lamp driver board's associated SCR turns on the expander board's lamp. When the lamp is on the opto isolated triac turns the relay on. The relay is toggling the banks of solenoids hot side while sharing a common solenoid driver transistor(which sinks low).
Can you hear the relay clicking? Can you check for the 43v? Bad opto isolated triac MOC3011? Jumper needs to be in too. It connects the 43v to the middle pin of the relay that switches to each bank side of solenoids.