On the original switch, each resistor (there are two in series) is about .8 ohms. If we find the potentiometer is capable of .8 and 1.6 then we have our low and medium and we can use the switch just as it is. He gave us the hint however that is not the way it works because the pot is used to control solid state devices internal to the controller (probably at much higher ohm values). Nothing that is easy is worth doing. WE can figure out how to adapt it. If not Tim, there is always this:
http://devestechnet.com/Home/Native12VUpgrade#heatersystemThe 6 volt motor is another story. I have one coming for testing to find out.
