Where is the heat sensor located that tells relays to turn on radiator fans? I see one under exhaust manifold on frt of motor, not sure if it's the one I'm looking for.

 

This is all done electronically through the PCM for when fans turn on and off. The PCM controls when to turn on and off the fans via coolant temp sensor located right by the thermostat (thermostat is located where the upper radiator hose connects to the engine)