Normally when you turn the key off the car will run for whatever your timer is set for or defaults to. Once it shuts off you simply turn the key back on to the accy position which activates the timer again and then turn the key back off. The timer is going to run for the prest time again, only this time the engine's not running, just the fan since it should be wired into an ignition circuit. When the timer counts down the ign will turn off and the fan with it.