You can use either pin 4 or 7, with pin 5 being the ground connection. When the selected pin is activated, it goes to +12V.
For a light tree, GrandPrix Race Manager will only provide a kick-off signal, and (optionally) an end of race signal. The light tree must be able to control the light sequence on its own.
For a solenoid, GrandPrix Race Manager will provide a trigger signal.
Note: You cannot use both a light tree and solenoid with the software, as the software has no idea when the lights hit green. However, your light tree may be able to trigger your solenoid.