How to Wire an Electric Fan With a Relay

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Converting your vehicle to an electric fan system has several benefits. For one, removing the fan that's mounted on the engine reduces parasitic drag and can increase horsepower. Also, the fans will only turn on when necessary, rather than running all the time. Plus, you can actually get a better cooling system out of the conversion. This article uses the example of a 1995 Chevrolet Silverado that has electric fans; here's how to wire the fans using a relay.

Things You'll Need

  • Wire cutters
  • Wire crimpers
  • Assistant
  • blue butt connectors
  • 12-volt test light
  • 30-amp relay
  • Red, black, green, yellow and brown 18-gauge wire, 20-foot lengths
  • On/off switch, 12 volts
  • Drill and drill bits
  • 3/8-inch ratchet and sockets
  • Ring terminals
  • Self-tapping screws
  • Blue spade connectors, male and female
  • Zip ties
  • Pop the hood and find a spot to mount the relay. This is probably easiest on the core support, as it's close to the fans as well as convenient for wiring.

  • Mount the relay to the mounting spot using the drill and self-tapping screw.

  • Ground each fan motor by running the black wire from the fan motor to the chassis of the vehicle, using a factory bolt if possible. Crimp a ring terminal to the end of the wire, and unbolt a bolt using the 3/8-inch ratchet and socket set. Do not tighten down this bolt yet, as you'll be using it again.

  • Crimp a female spade connector onto the end of the black wire using the wire strippers and wire crimper. Run the wire to the bolt where the fan motor is grounded, and crimp a ring terminal to that end. Now bolt everything to the chassis.

  • Connect the female spade connector on the black wire to the 86 pole of the relay.

  • Connect the red positive wire from the fan motor to the 87 pole of the relay by stripping the wire and crimping a female spade terminal onto the end of the wire.

  • Connect a female spade connector to the end of the red wire using the wire strippers and crimpers, and connect it to the 30 pole on the relay. Run the other end to the positive terminal on the battery, attach a ring terminal using the crimpers and wire strippers, and connect to the positive terminal using an open-end wrench.

  • Locate the air-conditioning compressor on the engine bay. Turn the vehicle on, and use the test light to probe the wires running out of the compressor. You want to find the positive wire that turns on whenever the A/C is turned on, so have an assistant turn the A/C on and off so you can be sure you know which wire is which.

  • Cut the positive wire going into the A/C compressor about 6 inches back from the plug. Strip 1/2 inch of wire from both cut ends.

  • Strip the end of the green wire using the wire strippers, and twist it together with one of the cut ends from the A/C compressor. Crimp one end of the blue butt connector onto the paired wires, and crimp the other end onto the remaining cut wire.

  • Run the rest of the green wire to the relay, making sure to keep it away from any moving or hot parts such as belts or hoses. Strip the end of the wire using the wire strippers, but do not connect to the relay yet.

  • Strip the end of the yellow wire and twist together with the green wire from the A/C compressor. Crimp a female spade connector onto the end of the wire combination. Plug that spade into the 85 pole on the relay.

  • Find a spot to mount the on/off switch. Mount it by drilling a hole.

  • Run the yellow wire into the cab compartment and to the dashboard. Strip the end of the wire, and connect a female spade connector to the end of the wire. Push it onto the middle pole of the switch.

  • Locate an ignition wire under the steering column using the test light. Turn the ignition key on and off until you find a wire that turns on only when the key is on.

  • Cut the ignition wire and connect a section of red wire to the ignition wire in the same manner in which you connected the green wire on the A/C compressor. Two wires will go into one end of the butt connector and one into the other.

  • Connect the red wire to the top pole of the switch using a female spade connector.

  • Connect one end of a section of black wire to the bottom post of the switch using a female spade connector. Run the other end of the wire to a piece of metal in the dash, and find a spot to bolt it for ground.

  • Strip the end of the black wire, and crimp a ring terminal to the end of the wire. Secure it to the piece of metal using the 3/8-inch ratchet and sockets.

  • Clean up all the wiring using the zip ties. Secure the lines to any other part of the vehicle that isn't moving, and make sure the wiring looks neat.

References

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