I fitted a Westfalia tow bar to my Audi A6, and I found the wiring instructions extremely difficult to follow, as there are no actual instructions, just pictograms. These often made no sense until explained, and sometimes had multiple possible meanings. I spent several hours trying to decrypt the 'instructions' and I still wasn't 100% sure I was correct, so I phoned them, and they were very helpful, we went through everything to confirm what I thought, and it turned out I was correct.
As far as I remember, the Westfalia instructions only show how to add the towbar module to the CAN gateway (using VCDS), this gets the trailer lights working, but loads of other ECU's also need recoding to get things working correctly. I got a list of the codes from Ross Tech.