I have an adjustable controller on my 350. It is set to come on about 205 and shut off at 190-195. I'm running a 180 thermostat. You want the fan cut-off temp high enough so that the fan will cut off under normal highway running.

If you have AC, you will need to run the fan any time the compressor is on or you will need a trinary switch to run the fan when the AC head pressure gets high.

A manual override switch could be handy, too.