This drawing should help you with trouble shooting although it for 1968 it’s correct for my 65 except for the ambient switch. My problem was the orange circuit to the master switch that during troubleshooting I determined was bad and kept blowing the fuse at the main fuse block when I turned the key on. Pontiac designed this so the blower always ran once the ignition was in the on or run position. I bypassed the master switch and installed a toggle switch and now the system works with it when its in the on position and the fuse is good now. For me I’m good with this configuration because if I don’t want the original blower running I can flip the switch off.
Bob
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