i have the flex-a-lite set up , it has a controller, everything wires into that controller will regulate fans for cooling engine and a/c, my advice before you do this is upgrade your battery cables all power and grounds, they talk about doing the big three , batt positive to alternator, ground from alt to batt , starter cable to batt , and engine ground to frame or body. you can look those up on youtube , but i have a 23 yr old truck , so i upgraded all cables to 1/0 heavy duty, that way there will be no power drop anywhere , also make sure you use 12 gauge wire for your power source , there is a guy on youtube that did it all the wrong way and almost burned up his wiring harness, and while in thinking about it you might want to upgrade your alternator to a 140 amp, the fans will pull alot of amps. thats why all the upgrades to run the fans and save your wiring harness.
if you dont have the flex-a-lite setup , painless wiring has a relay set up just for electric fans, i think it has 4 relays all wired ready to go.