From Porsche Club of America:

LINK

Quote:
Question:
I have heard MANY people talk about the problems they have had with the Cayenne and towing an enclosed trailer. I have a 20' enclosed with 15 or so running lights. I, like many others, can not get the "!" "check trailer lights" to clear or get the running lights to work.

So far the only solution has been to remove most of the lights and hope for the best. Is there a fix or update for this problem?

Answer:
Volkswagen has a adapter kit for trailers that have LED lights on their trailer. That might work for your trailer. Check with you local Volkswagen dealer for the adapter for the Touareg.

Peter Smith - PCA WebSite - 7/28/2006