Here's another option for a switch Link.

I just bought one of these. They are rheostat style switches (off-high and variable to low) and I measured the resistance as between 0.2 and 0.5 ohms on the coil. These have had some moisture on them, so need a little cleanup. I have an original "HEAT" backing plate that I'll use after a bit of restoration. I'm not sure if the resistance is correct for the heater motor (so it changes speed significantly, but I'll find out.

Wiring is pretty simple - Go from the accessory contact on the ignition switch (so you don't forget and leave the heater running with the engine off) thru the switch in series and to the motor. The ground lead from the motor should be connected under one of the mounting bolts for the heater, cleaned off so it makes good contact.

Kevin
1951 Chevy 3100 work truck
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1929 Ford pickup restored from the ground up. | 1929 Ford Special Coupe (First car)
Busting rust since the mid-60's
If you're smart enough to take it apart, you darn well better be smart enough to put it back together.