You need to get a thermostatic switch like this one: http://store.summitracing.com/partde...5&autoview=sku and wire it in to a relay to control the power to the fan itself. Ignition "switched" power should be used for the "hot" side so your fan doesn't run your battery down after you shut your engine off. This should have it's own seperate fuse also, based on the amperage requirement of your fan (5 to 10 amps higher than the fans actual rating to compensate for amperae surge at motor start up). Use appropriately gauged wire to handle this load also.