When installing an auxiliary fan or simply wiring the factory fan so that the driver can manually turn the fan on and off, make sure the fan is turning in the right direction. If the fan is not turning in the right direction, air will be blown away from the radiator, and will not help to cool the radiator. To check which way the air goes, just put your hand in front of the fan to make sure the air is blowing through the radiator. The fan will turn in either direction depending on which of the two wires the power is supplied to. There are two methods to wire the relay, one with manual control and one with automated control.