If i use a original ac harness and only have a heater now do i just cut off the wires i dont need? or do i need a harness for a non ac car?

The dash harnesses are the same. The switch and the resistors are different though. Just unplug the option A/C harness and hook the dash harness up as a non-A/C car. The wiring is the easy part.

It has been my experience that some 70-72 dash harnesses have provisions for A/C only (one large brown wire) and others have provisions for A/C and Heat only.