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Radiator fan ballast resistor replacement (DIY instructions)

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This is a revival of a post I made on PPBB on July 29, 2009:



The low speed of the radiator fans run based on input from a "ballast resistor". There is one resistor for each of the two radiator fans. These resistors have been known to fail in older cars. For details on how to easily diagnose and test the resistors, see my post "Radiator fan hack"

Follows are instructions for replacing the right resistor.


Access to the resistor and its plugs is from under the front right of the car and the front of the right wheel well. The ballast resistor is connected to the electrical system with a large plastic snap-together plug and connected to radiator fan wires with crimp connectors.


(1) Insert a jack stand will under the right side, front jacking point.

Important: Make sure the jack stand is secure. Your head is going to be under the front bumper for this procedure and it is imperative that the car not fall. It is always a good idea to have a backup means of support, such as placing a wheel under the side of the car.

Front right wheel well

(2) Remove the front right wheel.

(3) Undo the fasteners holding in the front of the right front wheel well liner. If you then pull back the wheel well liner you can see the wires for the resistor (green/white and black). The wires lead up to a big plastic electrical plug that is a bit hard to see but it is near the top of the wheel well, straight back against the front wall.

Old part behind wheel well liner - 1.png

(4) Unclip the electrical plug from the wall by sliding it against the wall towards the center of the car (away from you).

Electrical plug.png

The clips look like this once removed

Plug clip.png

Plug closeup.png

(5) Unplug the electrical plug by pressing the two tabs on the sides while pulling it apart.

Under the front right of the car

(6) Unclip the old ballast resistor by pulling it out of the clip. A new clip comes with the new resistor so you can remove the clip as well by sliding it upwards. Clip the new ballast resistor in its place.

Unclip resistor.png

(7) Follow the green/white and black wires from the old resistor up about 6" to find the place where the old (black and green) wires are crimped to the radiator fan wires. Cut the old wires, just above the crimp connector (the fattest part under the shrink wrap).

In this picture you can see what's under the old shrink wrap.

Old wires.png

(8) Strip the newly cut wires with a wire stripper, exposing approximately 6 mm of bare wire.

(9) Crimp on electrical butt connectors to the bare wires on the new ballast resistor. I got the connectors from Radio Shack ($1.99 for 20)

Butt connectors.png

(10) Cut two pieces of shrink wrap tubing (approximately 3 cm each) and place them over the ballast resistor wires.

(11) Crimp the other side of the butt connectors to the matching (green or black) wires coming from the radiator fan. Make sure you don't skip step 10 or you will have to cut the wires again.

Butt connectors installed.png

(12) Slide the shrink wrap tubing up over the crimp connectors and use a heat gun to shrink the tubing.

Shrink wrapped.png

(13) Make a mental note of the routing of the old ballast resistor wiring and pull it all out. Route the new resistor wiring the same way.

(14) Plug in the electrical connector and clip the electrical connector to the wall. You slide the connector along the wall towards you to clip it in place. If you hold a flashlight with your other hand, it is possible to see what you are doing.

(15) Test the operation of the ballast resistor. Make sure you remove the ballast resistor hack you may have performed on an earlier date before testing. Start the engine, turn on the A/C, verify that the right side fan is operating.

Remove old hack.png

(16) Replace the wheel well liner, wheel, remove the jack stand and take your car for a nice drive on the twisties.

Edited 1 time(s). Last edit at 06/04/2018 01:30PM by Boxsterra.(view changes)
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