How to Manually Turn on a Radiator Fan
by Don Bowman
Modifying the radiator fan to turn on manually is usually done because something in the system is not working properly, and the vehicle owner does not want to replace a part, usually due to the expense. Operating the fan manually is just as effective, and in some cases, moreso, since it won't be forgotten. If the fan is not turned on when the vehicle is at rest or moving slowly, the vehicle will overheat. The fan is not necessary as long as the vehicle is moving, and air is passing through the radiator.
Step 1
Cut the power and ground wire at the fan harness, leaving 6 inches or more to connect new wires. Tape the harness ends of the wire cut, using the electrical tape.
Step 2
Install the four-terminal relay to a solid mounting location as close to the radiator as possible. Use the ¼-inch drive ratchet and socket to loosen and tighten the mounting bolt. Mount the switch on or under the dash panel where accessible.
Step 3
Attach a spade-end crimp to one end of a 16-gauge wire. Attach it with the crimping tool and connect it to the negative terminal on the relay. Run enough wire to go through an access in the firewall to the switch and return to a good grounding location on the frame or engine. Cut the wire at the switch and attach two spade terminals to the wire. Attach them to the back of the switch. Attach the appropriate terminal to the loose end of the wire, and attach it to the frame or engine.
Step 4
Connect a 10-gauge wire from the positive terminal of the relay (shown on the relay diagram to go to component) to the positive wire on the fan. Use a spade terminal on the relay end and a butt connector on the fan side. Crimp the terminals with the crimping tool.
Step 5
Connect a 10-gauge wire from the negative wire at the fan to a good ground. Use a butt connector at the fan side and an appropriate terminal for the ground side. Disconnect the negative terminal on the battery.
Step 6
Connect a 10-gauge wire to the battery positive terminal using the appropriate terminal. Run the wire over to the relay and cut the wire allowing a small amount of slack. Cut two, 3-inch pieces of wire off the roll of wire, and strip the insulation off both ends of both wires. Attach a spade terminal on one end of both 3-inch pieces of wire.
Step 7
Strip the insulation off the opposite end of these wires. Strip the insulation off the end of the wire from the battery positive terminal. Install a butt connector on the end of this wire and crimp it.
Step 8
Insert the stripped ends of both short wires into the butt connector of the wire from the battery. Crimp both wires into the butt end. Connect the other ends of both short wires with the spade terminals to the remaining two terminals on the relay. Connect the positive terminal on the battery.
Things You'll Need
- Wire-crimping tool
- Assorted wire terminals
- One roll of 16-gauge wire
- One roll of 10-gauge wire
- One 4-terminal relay
- One electrical switch rated at 30 amps max
- One roll of electrical tape
- ¼-inch drive ratchet
- Set of ¼-inch drive sockets
Writer Bio
Don Bowman has been writing for various websites and several online magazines since 2008. He has owned an auto service facility since 1982 and has over 45 years of technical experience as a master ASE tech. Bowman has a business degree from Pennsylvania State University and was an officer in the U.S. Army (aircraft maintenance officer, pilot, six Air Medal awards, two tours Vietnam).
