Nacho, very interesting read at the Charger site! Also good to know that there are thermal switches for multi speed fans available.

I converted the temp settings on the first switch to F and found the following: LO - 180F ON, 170F OFF HI - 190ON, 180OFF. That's fairly similar to the values that I took a guess at.

FYI, I ran across a controller that might fit the bill. It has the ability to control the ON/OFF temps of single or dual fans and it doesn't need a separate sensor (only possible if you have a Dakota Digital dash). The P/N is PAC-2800BT. Since I already have a Dakota Digital VHX dash, I'm considering this controller instead of wiring something myself.

But I do appreciate your diagram and your input!