I don't believe that resistor is a variable type, just an alternate load for the motor. There's likely a potentiometer (variable resistor) inside the switch, although I have never taken one apart. So the slider would be inside, not on the external resistor.

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.