1972 Duster 340 M&H wiring harness

The AC clutch wire is a separate harness that plugs into 2 empty slots on one of the firewall connectors... usually the blower fan (green) wire is part of that harness too... that harness is available from Year One (M&H). Not sure about that plug... does it go to the firewall plug? If so tracking that down in the schematic may give a hint.