Hit the button too soon...

Anyway, it was obvious to me what was going on, I'd cut the wire and the fan took off and the light came on. It was only a matter of measuring the width of the pulses to figure out what they were doing. I could see the pulses from the ECM get wider when I turned the A/C on, then even wider as the temp needle went past 1/2 way.

I then used a function generator to simulate the ECM to make the FCM do what I wanted - THAT was a challenge.
But then the performance shop in ATL charged me only $50 to reprogram the ECM for a lower fan-on temperature. I then stopped by research into how to have a "dial it up on the dash" fan speed.