Three terminal ISC solenoids need one Auxiliary Output to open the solenoid and another Auxiliary Output to close it. When setting these outputs in the ISC section they are selected as a pair of drives.
Use an ohmmeter to find the common terminal (usually the centre). Figure 8.14 shows the schematic. Next measure the resistance between the common and remaining two terminals, this should be greater than 10 ohms. Apply +12V to the common terminal of the solenoid and ground one of the other terminals. If this terminal causes the valve to open, wire it to the first of the auxiliary output pair, wire it to the second of the auxiliary output pair.
Three terminal ISC Solenoid Wiring