The A/C power wire runs thru the same harness as the High Fan Relay. The red wire on the High Fan Relay is connected directly to the primary buss (battery). The green (usually) wire on the A/C low pressure switch is also the A/C power wire that activates the compressor. Sounds like these wires are coming together somewhere, either shorted together, on the wrong terminal, or thru a short in the High Fan Relay. This wiring harness, the relay, and the pressure switch are all located next to the firewall passenger side. The other wire on the A/C compressor plug is a ground. Originally grounded to a stand off on the intake manifold. This stand off is usually missing or broken off. I grounded mine to the A/C compressor mounting brace.