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pin 40 goes from the ECU to the A/C relay and the one at ECU pin 41 comes
from the A/C control head. From this I speculate that most of the time the
ECU will connect 40 and 41 internally unless it wants to turn off the A/C,
for instance if the "kickdown" switch is activated. I am guessing that 41
carries switched power from the A/C control head (12v when the A/C control
head wants the A/C to be on, 0v otherwise) and the ECU chooses to either
pass that along to 40 and power the A/C relay to pull in the compressor
clutch, or not.