I swapped a 1991 TPI harness into my 1985 TPI car. On the 91 harness the HVAC comes off it with a connector that has a black, red, and blue wire. The blue wire is small and about 16g. I still have the 1985 HVAC harness in place and wanted to just splice into the +/- power wires. What is the blue wire that comes out of the engine harness and into the HVAC wiring?

Here is a pic, hard to make out but the engine harness side has +/- wires and a blue wire.

 

I figured it out. The blue wire coming out of the engine harness goes to the AC system. I assume it is there to turn on the secondary fan when the AC comes on.