I only used the high speed setting on my fan. Power to it is fed a continous duty solenoid, like what you see inside a Warn winch solenoid pack. The solenoid is controlled by a cheap Flex-a-lite controller with a probe shoved into the rad fins.
Lately the controller has not been working right so I may replace with a temp probe in one of the rad hoses. I would lose my adjust ability though. The Flex-a-lite controller has an adjustemnt screw on it to adjust kick in/out up and down. A probe would just be at set temp.
I also have a 3 way switch on the console for the fan. Off/Force on/Auto