where is the temp sensor located that turns on the supplemental electric radiator fan? And is it a simple "on-off" device or can the temp be adjusted - either with a different sensor or in the computer program?

 

If you have the 5.9L or 5.2L it is located to the left of the thermostat Housing. It is small with two wires going to it and attached on the top. From there the computer reads the temp and triggers the auxiliary fan to come on when the temp is up. You can get a Programer to adjust the temp for when the fan comes on. It is computer controlled.