Clutch Fan!

An electric fan needs a controller. Hayden makes several models. The best type have a coolant temperature sensor that screws into a pipe thread (~1/4 NPT). Cheaper ones have a sensor you push into the radiator fins. I got a few of the better ones for $25 on rockauto a year or so ago, but usually see ~$55. The Hayden ones usually come with an integral relay and have an adjustment for the temperature setpoint. You could also wire to a manual switch in the cabin, if you want to play "man in the loop controller".

Simplest is to wire it to IGN1, so always on w/ the engine but not directly or you will melt your key switch and/or bulkhead connector. Use a relay. A cheapie fan can use a normal 40 A automotive relay. Bigger fans might need a bigger relay. My 02 Chrysler minivan uses a solid-state relay for the 2 fans, which should work (see rockauto). Same basic hookup as a normal auto relay.