How to Wire an On/Off Switch for an Auto Cool Fan

by Justin Cupler
itstillruns article image
toggle switch image by Sergey Danilov from

At times, your cooling fan stops working because a sensor has gone bad, but the fan works just fine. A way to get around this situation is to wire in an on and off switch. This switch works by eliminating the ground connection when it is switched "off" and reconnecting the ground when it is "on". The process of wiring this switch is relatively easy. You just need to know the correct steps.

Step 1

Locate a convenient pace to mount the switch. A good place is somewhere out of the way but still within reach. Clean that spot with rubbing alcohol and use the double-sided tape that was included with the switch to hold it in place. Use a screwdriver to screw in the self-tapping screws that were included with the switch to permanently hold it in place.

Step 2

Locate a 12-volt power source by using the multimeter. A good source close to the switch is the cigarette lighter. Cut the power wire leading to the lighter, then cut a half-inch of covering from either side of the cut.

Step 3

Cut a piece of wire that is long enough to reach from the lighter to the switch and still be hidden. Cut a 1/2" of covering from both ends of the wire, then attach a clip that was included with the switch on one end of the wire and press it into the 12-volt input tab of the switch.

Step 4

Twist the two ends of the lighter wire and the other end of the switch wire and solder them using solder and a soldering iron. Tape the wires with electrical tape.

Step 5

Cut three pieces of wire long enough to reach from the switch through the firewall to the front of the engine compartment. Remove 1/2" of covering from each end of both wires.

Step 6

Run the wires through the dashboard, hiding them as well as possible. Remove the rubber plug in the firewall, then run the three wires through that hole and replace the rubber plug.

Step 7

Run two wires to the fan motor. Cut the power and ground cables from the fan motor. Remove 1/2" of covering from the positive and negative wires running into the fan motor. Attach one of the new wires to the positive wire and one to the negative cable and solder them together. Protect them by covering them with electrical tape.

Step 8

Locate a body ground under the hood of the vehicle. A good way to locate a ground is to follow the ground cable of the battery.

Step 9

Remove the ground from the body using a ratchet and socket to loosen the nut. Connect the "eye" connector to the last remaining wire using the wire stripper to crimp the connector. Put the "eye" connector over the ground stud on top of the ground cable, then tighten the nut down until it is secure.

Step 10

Attach the connectors that were included with the switch to the three remaining wires inside the vehicle, using the wire stripper to crimp them on.

Step 11

Plug the connectors to the corresponding tabs on the switch. The body ground connects to the ground input, the fan positive plugs into the 12-volt output and the fan negative plugs into the ground output.

Step 12

Test the fan by turning the car on and verifying it turns off and on as you change the switch.

Step 13

Secure the wires using zip ties. Pay special attention to avoiding moving parts and keeping your feet under the dashboard.

More Articles

article divider