Controlling an electric fan can be as basic as using the properly sized wiring through a high-amp relay and a toggle switch on your dash. However, we suggest a thermostatic switch of some sort, as a toggle switch can be forgotten in the heat of stop and go traffic. A basic thermostatic switch can be inserted into the water jacket of the engine or into the radiator core. The Flex-a-lite variable-speed fan controller is just one option shown here. The controller senses coolant temperature at the radiator and can turn the fan speed on from 60 to 100 percent.