I assume your talking about http://www.thunderracing.com/catalog...&vid=3&pcid=96
SLP's manual fan control switch allows you to turn you car's electric coolant fans on manually, yet still retain stock fan operation. If you are sitting in traffic or at the track waiting in the staging lanes between rounds, you can click on your fans early to aid in keeping your engine operating efficiently and producing as much power as possible. With a flip of a switch, the fans will resume stock operation.
Ususally used to cool your engine while your waiting in the staging lanes. I hope thats the fans your talking about.