The one that I've never had too good of luck with is the type that use the probe that sticks into the radiator fins to read temperature.

The first time I used one was on an 82 Monte Carlo that I swapped a 350 into and put a set of Spal fans in it. Had a thick aftermarket aluminum radiator. It could very well have been where I placed the probe that gave me issues. I put it in the fins up high near the top of the radiator near the fill cap on it. Thinking back, that's not a good location, because if the coolant got low the sensor wouldn't read the correct temp, which would explain why the car would almost overheat sometimes before the fans would ever kick on, in the winter time none the less.

The second time I used one was in a 91 Toyota Pickup that I tore apart and rebuilt, it actually controlled the fans fine, but it control module the sensor was connected to, 2 of them burnt up within a couple months... I eventually hardwired that one in a similar way that the one is now wired in by Blazer.

I followed blazen’s steps for mounting and which fan to use then I got a controller with a probe that goes into the block. Used a separate relay off the controller for the fans (didn’t trust controller relay quality) I have a master power switch for the controller incase I need to kill the power (water or giant mud pit) and I have no complaints about it plus I was tired of going through clutch fans