The A/C wiring harness is a " STAND ALONE Harness ". I do know a 1970 Chevelle A/C harness is Different than a 1971,( 71s have relays under the glove box,,72s??? ) Not sure about 1972s. I would NOT mix & match a Different year A/C wiring harness.
NOTE: When I converted my 1971 Wagon to a 70( It was punched in the nose). I used all 1970 wiring. After I built the car and was getting the A/C up & running......... THATS when I found out about the different A/C harness.
YEP !....... Pull the dash apart remove the 1971 harness and install a 1970 A/C harness. GEE,,, Just think,,, While building the car the dash was out, The engine was out and the seats were out. Looking back,,, I guess I thought I was a " Know it all." I just add it to the list of " My screw / ups ".....
P.S. Removing the 1971 harness and installing the 1970
A/C harness, I got my 6 foot 4" buddy Scott Miller, He was tall and could lean over the " Covered up "..." Fresh Paint " and not mess it up. I would feed him the 71 to get it out and push the 70 in, through the firewall."
Scott laughed and called this a cluster ---- !