There is also a safety toggle switch in the middle. The ignition is cause by running 70 VDC through a 1/4 Watt 24 Ohm resistor. As you can see in the demo after the break this results in flames ...

But if the resistor burns out or wears out from corrosion, there is nothing to reduce the amount of voltage going to the blower motor for the lowest fan speed, so it will most likely get the ...