Adding a manual switch to an electric radiator fan is an economical way of keeping your car cool and in good condition. If you're rusty or new to this automotive element, here's a short rundown of how radiator fans work. Electric radiator fans operate when radiator temperature rises to preset heat range. When the radiator temperature lowers to a preset level, the electric fan turns off.
Adding a manual switch can essentially be a one-two punch, once you know what you're looking for. Open hood and look at front of car to locate radiator and fan inside engine compartment. If you are unable to find an electric fan attached to you radiator but there is a fan with a rubber belt around its pulley, then this article will not apply to your vehicle. If you are able to find an electric fan, then read on.
The fan will have electric wiring coming out of its motor and going into a wiring harness. This wiring harness is where you will concentrate your efforts. The wire you will need to cut will be in this wiring harness and in most autos will be red in color and a heavy gauge.
Step 1 - Wiring
The first step in adding a switch to a radiator fan is to disconnect the battery's negative terminal. Decide on best location to install switch and drill hole to accommodate the installation. Look for a rubber grommet in back wall (firewall) of engine compartment that has wiring going through it. This will be your install option to get your new wires through the firewall and behind dashboard. Now find the red wire that is connected to the motor of the electric fan.
With the help of a wire cutter, cut the wire at a distance of twelve inches from the start point. Attach an electrical connector at both ends of the wire and put a heat shrink over them. Add a new red 12AWG wire from positive battery connection to switch location. This wire will require a fuse to be installed in it to provide safety of the vehicle and protect against electrical shorts and possible fire. The safest location for the fuse is as close to the battery connection as possible or approximately 12 inches from the battery. Vehicle design will dictate fuse location in most installations.
Step 2 - Connecting the Switch
Connect red 12AWG wires from ends of wire previously cut. Double pole single throw switches have 6 terminals. You will use 4 of these and ignore the other two. Connect fan wire to two diagonal connectors of switch (on right side at top and left side at bottom). Connect the other wire coming from original cut to one of the center terminals of switch.
Connect the new fused wire to other center terminal. Install switch in chosen location. Secure all wiring where it will be safe from abrasion and rubbing on any part of auto. Plastic wire ties (zip ties) are great for this and most hardware and auto parts stores have them in stock.
Step 3 - Check Switch for Correct Wiring
Reconnect negative battery terminal and flip switch between positions. One way the fan should run, while flipped the other way fan should not run until radiator temperature is high enough to turn on fan. Label switch to indicate manual position. You now have a manual override for your fan. This is very useful when in stop/go traffic or when operating air conditioner while driving at low speeds to provide radiator cooling or even when car is not moving.
Since the air conditioner condenser is in front of radiator and also needs air flow across it to provide cooling of refrigerant this manual switch will aid in maintaining cooling ability of your air conditioner. Remember to turn off from manual override when shutting down your vehicle as the fan will continue running and drain your battery.