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Ballast resistor replacement

Old 05-04-2014, 03:33 PM
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Porschey747's Avatar
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Default Replace ballast resistors

I have just finished replacing my ballast resistor on the passenger side and I've done it a lot cheaper than using the genuine Porsche Ballast resistor. I'll do a step by step guide but if anyone wants any help, message me.

I'll describe the passenger side but obviously if yours is drivers side then alter as required.

Before you start, go to RS or similar and get a 0.5R 100W (RS code 188-071) resistor. This will cost you about ú5 inc VAT.

1. Remove the wheel and support on a suitable axle stand.
2. Remove the wheel arch liner which will give you access to the ballast resistor wiring.
3. You should see the resistor on its clamp with the wiring coming from it.
4. I would disconnect the battery for safety at this point.
5. Cut the wiring as close to the old ballast resistor as possible.
6. Remove the old resistor and bin it.
7. Identify the three wires (green, white and green/white).
Green = Low speed fan supply
White = High speed fan supply
Green/White = Output to fan motor
8. I suggest you get hold of a good soldering iron, you will need something quite powerful or use good quality crimp connectors and cover all joints with heatshrink, the stuff with adhesive in is the best choice.
9. Solder the White and Green/White wires to one side of the resistor and then cover with heatshrink.
10. Solder the Green wire to the OTHER end of the resistor and cover the joint with heatshrink.
11. Drill a couple of holes so you mount the new resistor where the old one used to be. Make sure its in the airflow of the fan.

To test the new resistor.

Reconnect the battery and make sure all fuses are good.

First of all you need to know where the relays are. Look under the dash above the fusebox and you'll see a row of grey relays (each is marked with a large 53).

Working front to back, they are :

1. Not important for this
2. Passenger side low speed
3. Passenger side high speed
4. Drivers side low speed
5. Drivers side high speed

OK, choose which relay you need to pull, I would suggest high speed first of all.

Once you've pulled the relay, make a short piece of wire ( 100mm) and crimp a blade type connector one each end. Use this to "jump" the relay.

Connect from the top connection (vertical slot) to the bottom horizontal slot. The fan should run at full speed (you'll hear it).

OK, now remove the link and replace the relay.

Do the same again for the low speed and you should hear the fan run at a lower speed.

Remove the link wire and replace all relays.

Replace the wheel liner and roadwheel.

Start the car and put the a/c on and set it to the lowest temperature, give it a few seconds and you should hear both front fans running at low speed.

Hopefully the two pictures will work. One shows the new resistor in place and the other shows the front now I've fitted some mesh and DRL's.

If anyone has any questions or needs a hand, message me.

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Old 05-14-2014, 06:06 PM
Join Date: Dec 2011
Location: Mason, Ohio
Posts: 102

Thanks for this write-up! I plan to try this this weekend.
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Old 12-01-2015, 03:35 PM
Sean Whitcomb
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Originally Posted by yank_my_chain View Post
Thanks for this write-up! I plan to try this this weekend.
I did this fix last week.

Both old resistors
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New ones
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Car runs much cooler now.
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Been tracking it for about a week now, and it runs 15-30 degrees cooler then it has since I bought it in Decenber of 2013.
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Old 07-17-2017, 11:32 PM
Join Date: Jan 2014
Location: Houston
Posts: 43

I realize this is an old thread but I hope someone can help me.

I recently replaced the driver's side ballast resistor in my 2001 996 cabriolet. I noticed that both driver and passenger side triangular shaped removable covers are missing from the underside of my car - this probably explains why one resistor went bad due to cold rain.

I haven't been able to find a part number for the cover. Can anyone guide me to a resource with part numbers for under body parts?

Thanks in advance!
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Old 07-18-2017, 12:10 AM
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Location: Capital Region of NY
Posts: 796

If you've got the pdf version of the parts catalog, the underbody parts are in there, somewhere around page 240.

If you need the pdf, it is here:
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Old 07-19-2017, 11:02 PM
Join Date: Jan 2014
Location: Houston
Posts: 43

Originally Posted by KoB View Post
If you've got the pdf version of the parts catalog, the underbody parts are in there, somewhere around page 240.

If you need the pdf, it is here:

Thank you so much - this is perfect and I really appreciate your help!
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Old 01-30-2018, 12:31 AM
Join Date: Jan 2014
Location: Houston
Posts: 43

Originally Posted by ivangene View Post
keep in mind these little buggers get bloody hot

one the reason they might fail seems to be that they get super cooled with water splashing on them causing internal fracturing and thus failing

Yes nothing special about them other than the shape/size/availability
you could solder about anything in its place to reduce the voltage as long as it can be mounted safely, not come in contact with any surrounding parts and handle the power requirements

My son just went through this on a computer monitor he bought that had a blown capacitor - the part was sourced out of Canada for $2 and not easy to find, but at the end of the day it fit the needs and solved the problem.
Sorry to bring up this old topic, but I have a question about the missing cover (if there ever was one). I recently had to replace one of my ballast resistors and would like to avoid having to do it again - especially if it's because it got super cooled from splashing rain. Is there supposed to be a louvered cover to protect the ballast resistor, or is it supposed to stay open to allow hot radiator air to flow through? If it is supposed to be covered, could anyone tell me the part number or take a photo to show me how it's supposed to look?

Thank you!!

missing cover?
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Old 01-30-2018, 01:09 AM
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It's supposed to be open like you said to let the hot air vent.
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Old 01-30-2018, 11:35 PM
Join Date: Jan 2014
Location: Houston
Posts: 43

Ahsai, thank you!
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Old 07-23-2018, 10:00 PM
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Join Date: Aug 2015
Location: SF Bay Area
Posts: 95

Nothing to add to the electrical info already in this thread but I did try a different mechanical solution to mounting the non OE resistors. The OEM resistors have exactly the same OD as 1/2" copper pipe which gave me an idea...a few pop rivets and some bent 3/4" pipe brackets later....

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