Hugh,

I don't know what you have or how it was factory wired. I will say this. You mention only three wires. If the motor is supplied with power (fused) through one wire, that leaves two remaining.

Unless the ON/OFF switch completes a path to ground, I would surmise that the switch requires two wires from the motor to complete a circuit to turn the motor on.

This is only a guesstimate on my part. Good luck and welcome to the Stovebolt.