ABS/PSM light from a new LED 3rd brake light

Hi everyone, Recently I picked up a 2004 C4S. I've gotten to work personalizing her for this summer. I've finished installing LED lights on the exterior of my car, except for the headlights. However, when I installed the third brake light yesterday; a clear eBay LED one, I noticed that when I turn on my low beams/parking lights it throws an ABS/PSM fault. I tried to reserach this but I can't find a clear answer (reverse polarity, wire in a resistor, some other fault?) , I am in no way a mechanic. Can you guys help clear this up for me?

Since the brake light doesn't come on when you turn the lights on, it sounds like there is something else going on. But to diagnose I would do this: 1) Unplug the new 3rd brake light and see if the problem persists. If it does, it isn't the brake light. 2) You could reinstall the old light and see if the problem goes away. If it does go away, I would return the LED lights to where they were purchased. If the problem persists, go over all the things you did to the car before you changed the light. That might point to a better answer.

^^ What he said ^^

You didn't actually say if the new third brake light is working, I just last week replaced some of the bulbs in mine and found that some of the insulation on the wiring had flaked off and shorted causing the fuse to blow and then got ABS/PSM fault, I must say that old third brake light was the most brittle piece of plastic I've found on my car and I've found allot of that, it practically fell apart in my hand

Quotes source post: 20443906

To the OP, as noted check for wiring faults where the wire flexes, where it meets the plug and the contacts inside the plug. Also, avoid no name eBay goods....sorry, but that is based on others' experience. @theBlitz, those snap fit housings are pretty bad aren't they? After trying to replace a few bulbs, and having my housing's tabs break in the process, I decided on Sylvania 194 LED's and glued the housings together w/ 3M 5200 making it essentially a sealed unit. I also potted the conductors in the housing with epoxy as they were becoming loose in the aged plastic. I burned in the LED's first to try and shake out any w/ infant mortality knowing the unit will be sealed. Worked so well I did both units on the 996 and the Boxster S. Brighter lamps also.

OP - All these clues are spot on. A bad bulb or electrical connection with any of the brake lights will always cause an ABS/PSM light. Plug the old brake light in and check. As long as the old 3rd brake light was good previously, you’ll have isolated a culprit.

Although the following post is unrelated: PSA - ReTrofit HID and 996.2 halogen - battery oil spoiler - Rennlist - Porsche Discussion Forums It is good reading as I have concluded that the 996 has a sensitive electrical system, likely related to CANBUS. As stated in the attached thread, I installed HID's on a halogen car and had a number of different faults. The worst one was the spoiler would deploy and keep deploying causing grinding noises. Took me a while to figure this out. As per the thread, I replaced the HID's with H7 halogens and I never had another spoiler fault. My point in this, I would replace every bulb possible back to stock and then try to figure out the fault. Although I'm a big proponent of LED's and have changed, upgraded etc. etc. on modern and vintage cars, I've decided to leave the 996 alone with all bulbs stock as the LED's seem to create a number of very unpredictable gremlins. And, yes, load resistors and other approaches can correct the issues, I feel it will just become another maintenance item with little reward. At my old house, I updated all my home lights, landscape lighting, everything to 5000K LED's. Well, when we moved, we purchased a home with a high end reno and very expensive light fixtures. There was not one 5000K fixture. Everything was 3500K and looked like incandescent bulbs. I think it is softer on the eyes and makes things more visible. For this reason my interest in 5000K LED's has also waned on cars.