72 demon A/C electrical help

the resistors are mounted in the case to keep them cool. Those create the various fan speeds . The fan switch selects the resistors so the wiring does go "from to" with or without a/c. There are differences though since non a/c wouldn't have the vacuum/electrical switch block. You'll need the correct harness. 73 and later is different, 67 is different. I don't know 68 through 72 are the same.
That's all I do and don't know. Hope it helps