[Barnsnake]

Why put the thermal switch for the fan in exit side of the radiator? The temperature of the radiator is of secondary importance. It's the temperature of the engine that matters.
By the time the temperature on the "cold" side of the radiator reaches the trigger point, the water coming from the engine would be critically hot (assuming the radiator is working).
There's generally an extra tapped hole in the intake water passage near the thermostat. Put the fan trigger switch there. If you are using one of those between-the-fins radiator temp switches, put it as close to the incoming water as possible.