C&C calls it "arc good" I think......it is looking for a contact closure from the plasma indicating that the plasma has transferred (and current is flowing) to the plate. The output from the 45 are the pins on the rear connector labeled "arc transfer" or "machine motion". These connections are made from an internal mechanical relay that closes when the arc is cutting metal, and opens when the cutting stops.
Pins 3 and 4 are the plasma start input.....with the machine torch installed, connect 3 and 4 and the plasma will start, disconnect an it will stop. These connections are disabled when a hand torch is installed for safety reasons.
Good luck, Jim Colt