Water temp should be judged at highest temp location, fan control from an same area-----like top of intake and or thermostat housing. That water pump fitting is for an return from heater core hose. The location of a fan sensor in the coolest part of the system will be inaccurate, and any relays/switches that are connected to it will be in reverse pattern to normal system --------

However---------you could make it work if you used some switches/relays set up around ambient air temps to run fans when water was a few degrees above that. It just isn't the most effient/logical way to do it--