Not sure if this has been mentioned already or not, but its also very easy to let the PCM do the fan "switching" for you. Especially if you already have a custom tune done to your computer.
I've set this up with my computer already and just tapped into that pin to switch on the fan. I can set on/off temps for both fans (seperate pins) to switch them on and off, A/C settings, set a period of time after the truck has been turned off to cool down to a certain temp (whichever comes first) and even compensate during idle for the extra load the fans put on the alternator.
It only requires a few "female" pins, some wire and a couple relays. Then you just need someone to tune your computer. Anyone like wait4me can do this.
Only works for 2001+ trucks though and may be cheaper then buying switches and temp controllers. And its reliable as stock in the end.
How to set up the stock PCM to control E-fans
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