If the switch doesn't work, I'm not out anything, it was free. Although,it did come from a GMC, so it should work, right?
I'm still using the old 6 volt heater motor on the low speed setting. It does travel fast, but so far it seems to be holding up. I don't run it very long, just enough to take the chill out of the air. When it finally blows up, I'll get the Grainger motor.
I don't like to use resistors, because of the heat problem. I had a resistor in line to the heater switch, but it got so hot that it melted the insulation off the wires connected to it.

But, I did use a Runtz resistor on the gas gauge.