DIS “Bulb Out” with LED license plate lights?

12 11 2008

NOTE: We do NOT carry the license plate LEDs or resistors.

Some of you may remember my post on LED license plate light replacements. Until recently, I haven’t had any issues with bulb out indicators on my B6 S4. I’d say the bulbs were fine for about six months, then I’d get random warnings from the DIS when I started the car. Sometimes they’d go away, other times they’d stay on. This became increasingly more bothersome so I did a little research.

As you all know, LEDs have less resistance than a typical filament based bulb. The DIS system monitors bulbs by checking their current resistance against a known parameter; when the values don’t coincide the system shows you an error.

To solve this little quirk we need to supply the system with an acceptable value. One option is to purchase new LEDs with built in resistors…at $40-50 for two, I said “Pass!”. Another option is to add a resistor inline to “simulate” the correct value.

I purchased 25 Ohm, 25 Watt load resistor to add inline to my license plate light wiring. To install this, I removed the trunk lid’s lining. It was secured by approximately eight clips and two screws (one inside the emergency escape handle, another in the opposite handle). Once I removed the lining I unplugged the license plate light harness.

The harness is made up of four wires: brown, gray, brown, brown/blue striped. I clipped the first set of brown and gray wires and sodered one end of the resistor inline to the brown side and the remaining end to the gray side. Afterwards, I added a little bit of electrical tape to protect the soder and wires from each other.

Finally, I needed to mount the resistor. Keep in mind, this resistor gets HOT, so don’t touch it! I choose to attach the resistor on the inside of one of the trunk panels with some high temp RTV silcone. I clamped the resistor down and let it dry. That’s it. DIS…gone!