Foot Switch, connector wiring

All three wires going into the connector in the rear of the Surgistat II ESU, have been pulled out of the Round, 4 pin connector. The connector is labeled labeled : A,B,C,D. The three wires coming in from the footswitch are: Black, White and Green. B is open and not used for any connection. I can't find any documentation/schematic on the wiring. Any info would help. TKS