The temp sensor is either a variable resistance unit or a simple switch. If you have gauges beyond a fuel gauge, you will have the variable resistor unit. Warning lights get the switch.
I would not use either to operate an electric fan as that was not their designed purpose and you might not get the results you expect.
Most aftermarket fan 'kits' will have a sensor that can be tie-wrapped or taped to the upper radiator hose. The contact with the hose will allow the sensor to 'know' the coolant temperature and operate the fan as needed. I expect you could find other sensors that could be immersed in the coolant via a freeze plug or a 'tee' (not good as flow is limited) or perhaps drilled and tapped into the thermostat housing, or even a replacement housing with sensor mounted. I haven't looked.
I would not use the gauge sensor nor the computer sensor(used for cold fast idle) out of concern of damaging the 'works' somehow.
tom
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