How to Wire a 12 Volt Electric Cooling Fan

Written by william kinsey
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How to Wire a 12 Volt Electric Cooling Fan
(Jupiterimages/Comstock/Getty Images)

Connecting a 12 volt cooling fan to a vehicle electrical system requires time, patience and a little electrical knowledge. The fan must connect to both the battery and the thermostat switch so that when the engine reaches a certain temperature, the switch will turn the fan on. Once the fan is on, air flow through the radiator will increase, reducing the engine temperature. Newer model cars use a fan relay to turn the fan on. The relay is controlled by the vehicle's on-board computer.

Skill level:
Moderately Challenging

Things you need

  • 12 volt cooling fan and wiring harness
  • Fan control relay
  • Temperature switch

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  1. 1

    Connect the positive wire of the fan to the positive post of the battery. This may require adding a longer piece of wire to the fan to reach the battery. This can be done by cutting a longer piece of wire and stripping 1/2 of an inch of insulation off of both ends. Connect one end to the positive fan wire and connect the other end to the positive terminal of the battery.

  2. 2

    Connect the black ground wire of the fan to the thermostat switch. Most old thermostat switches have only one terminal. Those switches are designed to connect the negative terminal of the fan to ground to complete the circuit. Newer vehicles have the thermostat wired to the computer and the fan is wired to a fan relay which is controlled by the computer.

  3. 3

    Start the engine and wait for the engine to reach normal operating temperature. Watch to verify that the fan comes on.

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