How to Wire Your Electric Fan Controller

By January 1, 2014Electrical

There are a few ways to wire your new electric cooling fan depending on how much control you want over the engine temperature. Your kit most likely came with a controller specifically made for your fan and in Part 1, Install an Electric Fan for Increased Power and Cooling, we went over how to install the new fan and mount the controller nearby in the engine bay.

Now we’re going to wire it all up based on the typical controller that’s normally included. Performing the wiring on your new electric fan may sound like a daunting task, especially if you’ve never done any wiring, but, it’s not. We’re going to wire them so the fan turns off when the ignition is turned off. Remember to use heat shrink tubing for all your connections to protect them from environmental elements. With thinner wires (like fan motor wires), an additional tip is to strip an additional 1/8″ of insulation and fold them over to increase the thickness of the wire sliding into the butt connector.

Wiring the Controller

Electric Fan Controller Wiring Diagram

Photo credit: Flex-a-lite

For this tutorial, we’ll be using the controller that comes with the Flex-a-lite #185 fan as an example. Wire colors may vary depending on your specific kit. Some controllers like the one pictured above accept spade connectors at their terminals while others (as shown below) also have short wires coming out (pre-wired) where you have to use butt connectors to join wires.

The controller pictured below is an example of a controller that is both pre-wired and also accepts spade connectors. It is a variable speed controller by Flex-a-lite (VSC #31165).

Electric Fan Variable Speed Controller Wiring Diagram

Photo credit: Flex-a-lite

1. Connect the Fan Motor Power Leads to the Controller

Once you’ve mounted the controller and have the fan/shroud combination securely mounted, route the two motor power leads from the fan to the controller, leaving just a little slack to allow for motor/radiator movement. If your particular controller has short wires coming out of it rather than spade terminals, chances are you won’t have enough wire length to join the short wire coming out of the controller to meet the fan motor wire. If that’s the case you’ll have to splice in or butt connect an additional length of wire between the two.

Our example controller requires spade connectors on the wire endings that go into to the controller so you can cut the length you need. Follow the steps below to install spade connectors on the wires and connect them to the controller.

  • Strip the blue and black wires coming from the fan motor 1/4″ from their ends. Twist each of the wire ends tight and fold them over like we mentioned above to increase the thickness.
  • Strip the 10-gauge black and red wires supplied with the kit, 1/4″ from one end. Twist the wire ends tight.
  • Crimp a butt connector to the blue fan motor wire, sliding the wire into the connector until the insulation contacts the metal inside the connector. Crimp the 10-gauge red wire into the other end of the butt connector making one long wire.
  • Do the same with the black wires.
  • Route the wires from the fan to the controller and cut them to the proper length.
  • Strip 3/8″ of the insulation from both the newly cut red and black wires and twist the ends.
  • Insert the red wire into a spade connector until the insulation contacts the metal insert. Crimp firmly but not enough to deform the connector. Alternatively, if your controller is already pre-wired, use a butt connector to join the red wire from the controller to the blue fan motor wire.
  • Do the same with the black wire.
  • If your controller accepts spade connectors, slide red and black wires with the spade connectors on them onto the correct spade lugs on the controller.

2. Connect Switching/Ignition Positive Power

This is the tricky part. Most of us don’t want the fans running our batteries down after the ignition is off, so we connect the switching power to a switched source. But where? That’s going to depend on the car, but for this tutorial, we’re going to use a switched accessory position on the fuse panel in the car, because it’s the easiest. On older cars, you can go directly to the starter solenoid.

  • Route a length of 16-gauge red wire from the controller to the fuse panel inside the car, tying it away from exhaust components and moving parts. Be sure to go through a hole in the bulkhead with a rubber grommet to prevent shorts.
  • Attach a spade connector to the controller side and connect it to the correct terminal.
  • Locate a fuse for a circuit you know is only powered when the engine is running, such as the ECU/TCU/Cruise Control/etc.
  • Remove the fuse, install the fuse piggyback, and reinstall the fuse.
  • Attach a spade connector to the end of the wire and connect it to the piggyback.

3. Connect Controller Power and Place the Temperature Probe

  • Remove the fuse from the power lead fuse holder.
  • Route two lengths of 10-gauge wire, both red and black from the controller module to the battery. If you have to go through the bulkhead (for a battery located in the trunk), try to go through an opening with a grommet. Be sure to route and zip-tie the wires away from moving or hot parts.
  • Attach large ring terminals to the battery side of both wires and spade connectors to the controller side. If your controller is pre-wired, use butt connectors instead.
  • Plug the red and black wires into the controller terminal lugs according to your instructions.
  • Attach the battery end of the black wire to the negative battery terminal or ground using the ring terminal.
  • Attach the battery end of the red wire to the positive battery terminal using the ring terminal.
  • Insert the fuse into the fuseholder.
  • Locate the radiator inlet and slide the temperature probe between two of the cooling tubes within two inches of the inlet. It may be easier to create a hole with a punch tool first before sliding in the temperature probe.

4. Adjust the Controller for Desired Temperature

If you disconnected any hoses from the radiator or drained coolant to install the fan, remember to reconnect them and refill the radiator before proceeding.

Turn the knob fully clockwise, carefully. Start the engine and allow it to warm up. When the engine reaches the desired temperature (use either the temperature gauge or an external thermometer), turn the knob counter-clockwise until the fan turns on. You’re done – it will now turn on at this temperature setting!

All of the wiring above is mandatory with pretty much any electric fan controller you get. At this point you can tidy up your wires, check that all connectors have heat shrink tubing on them and that none of the wires are able to rub against sharp edges or get pinched when the hood is opened or closed. Make sure you zip-tie the wires away from hot exhaust components as well. You’re now ready to go out and chew some asphault!

Optional Wiring Add-ons

Below are some additional wiring options to enhance your install or meet any specific requirements you have.

1. Mount and Connect the Manual Override Switch (Optional)

The manual override switch lets you turn the fan on manually if you feel the need. It isn’t necessary. If you plan on omitting it, you can skip this step. If you want to include this option you need to first decide whether you want constant or switched power to the override switch.

  • Mount the switch somewhere easily accessible from inside the car but where it isn’t going to be accidentally hit.
  • For the ground use a piece of black 10-gauge wire, strip 3/8″ from one end and install a spade connector, connecting it to the correct terminal lug on the switch.
  • Find a good ground under the dash (like the steering column or brake pedal assembly) and cut the black wire to length, crimping a ring terminal to the end. Attach the terminal to the ground.
  • Use another piece of 10-gauge wire between the switch and the controller, preferably other than black (yellow is good). Strip 3/8″ from the switch side, crimp a spade connector on it and connect it to the correct terminal lug on the switch.
  • Safely route this wire through the firewall, zip tying it away from hazards such as moving parts and exhaust system components to the controller. Cut this wire to length, strip it and crimp a spade connector to it in order to slide it into the right terminal lug on the controller.
  • Locate the inside fuse panel and route a piece of 10-gauge red wire from the switch to the panel.
  • Attach a spade connector to both ends after safely securing the wire away from moving parts and connect the switch end to the correct terminal on the switch.
  • For the other end, locate the stereo/radio/accessory fuse (for switched or ignition positive power) or battery terminal (for constant power). If using switched power, remove the fuse, install the fuse piggyback connector and reinstall the fuse and connect the wire to the piggyback. If using constant power, plug the spade connector into the lug labeled “Batt”.

2. Connecting the A/C Bypass or Override (Optional)

Typically, we want the fans to come on when the air conditioning is running, but having an A/C override or bypass is optional. Here’s how to perform the wiring on typical controllers if you want this feature.

  • Locate the circuit that energizes the fan clutch. You will need to determine if it goes to ground or positive when energizing as this will affect where you connect the wire.
  • Many controllers require that you identify and use the positive signal. Use a three-way connector to tap into the clutch trigger AWAY from the compressor and belt(s).
  • Route the newly tapped wire to the controller and into the correct terminal.
  • If your controller accepts either positive or negative A/C clutch triggering, be sure to use only one of these, NOT BOTH.

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