Hi Bob,
I traced it out and it is connected to the heater. Glad you mentioned that because I found the wires had been cut and twisted back together on the firewall by the heater- no tape, just a twist. I'll have to fix that before winter, since I'm in central Texas maybe not.
I turned the switch - I didn't do that before because it looked like it might have been some type of sensor. It turns easily and has four obvious detents when you turn it. Like 3 run positions and an off. The coils at the back of the switch inside the ceramic enclosure puzzle me. Are they resistance coils or some type of thermostat limiter? Do you know?
Regards,
David