Shoot its really hard to tell from that pic. I don't see why you'd have to buy a solenoid. You should be able to screw the
fitting right into the side of the regulator side.
Here's how i did my 1st generation ARB compressor. But maybe they've changed them that much to where it's way different now. You cannot see the regulator cause its on the bottom of the air quick disconnect. The piece the quick disconnect is connected to has 2 ports.
