i know a guy that wired his efans with the o2 sensors, which means that as soon as he turns on the truck, the fans start up. Is there any thing that could go wrong with wiring like that? Im going to install my fans this week and was going to get a harness from nelson, but if it will work like the way he did it, ill wire it like that and save the money for something else.

 

You don't need the fans running all the time. If you wire them into the PCM like the Nelson harness does (there are others that have made their own harness too), they will run only when they need to and put less wear on the fan motors. Another advantage is that you get different running combinations and different fan speeds with difference combinations of coolant temp and a/c statuses.