Using the Factory FC3S Thermoswitch to Control an Electric Fan

You can use the factory thermoswitch that can be found in the thermostat housing of automatic model FCs from 86-88 (S4) to control an aftermarket electric fan as follows:

S5 models (89-91) use a more conventional thermoswitch that has no continuity to ground until coolant temperature reaches 207 F or more. A more basic relay setup can be used in this case.