[hatzie]

Looks like you have a compressor cycling thermal cutoff switch with a capillary tube in the Evaporator. There should be a Low pressure cutoff switch on the accumulator as well. The aftermarket compressor and or hoses likely has provision for a high pressure cutout switch. If you're running R134a you'll want to add a HPCO switch in series with the LPCO and thermal switches because it has a tendency to run much higher pressures than R12 or HC blends.
I'd use a relay to offload the control amperage to the actual compressor clutch so the high amp load of engaging the electromagnet is run through an easy to replace $1.25 relay rather than the HVAC controls and the LPCO and Thermal switches.

Get a relay socket rather than using 1/4" disconnects. It makes the wiring job look better and it's much easier to replace the relay when and if it needs to be done.
Run a ground in series through the LPCO, HPCO, and Thermal switch to terminal 85 of a Mini ISO Bosch Automotive relay.
Run the Green AC compressor "on" wire from the HVAC control panel to terminal 86 of the same relay.
Run a 14ga wire through a 16ga fusible link or a 20A ATC fuse from the J stud on the firewall to the relay common terminal 30.
Run a 14ga wire from relay terminal 87 (normally open) to the actual compressor clutch plug.