Here is a picture of the compressor fan motor you can see on the left of the above circuit diagram:
That connector test connected to rad fan motor connector ( follow the red wire from the upper right at the radiator to the lower left):
Here is the switch temporarily wired up through the firewall:
It works! But as I expected, the compressor fan connector only gets power when the air conditioner is turned on. That is not a very desirable set up. But it works, and it will be easily reversed when finished.