Joe's Great A/C Thread leaves a lot of speculation, and the links to the NB diagrams are broken.
I'd like to reopen this topic and come to consensus.
Here is the A/C system wiring diagram for a 99
If I am reading correctly, it appears that I can jumper 1P to 1I and 1S. If I do so, it looks like the a/c fan and a/c comp clutch relay coils will take a ground path through the pressure switch, the a/c amplifier, the a/c dash pushbutton, and the fan switch, finally getting to a chassis ground behind the dash.
This may work fine. Or it may not. I don't know.
I was considering trying something else. Can/Should I use a couple transistors in this manner?
Bottom line is I want the a/c to function, and I don't want to use any I/O on the MS itself.
Comments, opinion, wild speculation all appreciated.