smk

Thanks in advance as I've searched the other towing related and lighting related posts and not able to fully comprehend. After 15 years without the 7pin connector being attached to the factory setup, I finally purchased and installed only to not get results I was looking for.

Any thoughts on what dealer tells me related to getting my lights working, and what I actually need to do?

"4. The tow control unit has a constant fault for the right trailer light with no trailer attached. P&A’d a new control unit.$925 parts and labor"

SMK - 2004 CTT - 267K

brett968

Remove the rear bumper cover and check the towing harness for damage. The harness tends to chafe on the passenger's side near where it enters the body (IIRC), leading to shorts/breaks in the wiring.

slavie

Assuming they tested it correctly and with no evidence to the contrary, I see no reason to doubt their diagnostic.
You could try to confirm the fault with a multi-meter, but that requires a multi-meter and some knowledge of what to do with one.
Or, take it to an indy shop for diagnostic. Though it's difficult to find a tech that's good at diagnosing electrical problems.
If it were my money, I'd get a used tow module from eBay for $50. No programming needed. They are a pain to install though, as you have to remove the rear right interior quarter panel.

Pillow

Agreed, but be sure to get the year specific module as they are all not the same. The Touareg is exactly the same parts, maybe Q7 as well.

I would just put a nused harness in at the same time. Mostly likely as said above, it is a chewed up wire.

Pulling the bumper cover is not that hard and just do both while you are there.

5l32v4c

In my experience getting a 7-pin setup for my '08, try to maybe find a used tow control module (located behind RHS trunk panel). There are variations so make sure to get a good match. I found one for $65 on ebay - just search for model # i.e. 7L0 907 383 (leave the last letter off). As someone else mentioned, they are common across Cayennes, Touaregs and Q7s. If you call a wrecker, they likely won't know what you're talking about. Installation should be plug & play. As for the wiring, a new harness is around $400-500 new and almost impossible to find used. Good luck!

brett968

True, they are rare--although I retrofitted my Cayenne with the towing package using an eBay sourced used harness. It was frayed in the same spot that others have experienced. It took 15-20 minutes to perform a proper repair. Any damage that OP finds in the harness should be straightforward to address. A replacement harness should not be needed.

A towing module fault code that indicates a signal fault is far more likely to be the result of a wiring problem than a defective towing module, especially considering these harnesses are notorious for chafing in the same spot. Unless the dealership stated that they checked the wiring and did a proper diagnosis, I would assume they didn't. Sorry, I don't have much faith in most dealership techs, particularly when it comes to diagnosis.

Pillow

The last letter indicates what year the module is from. Very very important to match this up. 09-10 has the last letter N.

Hit the junkyard for Touaregs! They are dying at a rapid rate and can be found in the pull-a-parts.

5l32v4c

The last letter is important; you certainly don't want to get an older revision. Leaving the last letter off while searching the interwebs for a used one will, however, increase your chances of finding one. Sorry if that was misleading.

smk

Thanks all. Indy shop was checking something else and found several bulbs out. Replaced them and found voltage on all pins. I believe trailer also has some led lights.

what’s name of one of those higher resistance adapters I can try?

will also check harness and check out new module.

Pillow

Try it first. Mine work fine with LEDs, but I used commercial truck LED replacements.