I want to tow a very small trailer with my 04 allroad. The hitch is hooked up already, but any ideas on where to get an adapter to fit the already existing Audi (but European spec) trailer light hookup to a four prong US one?

 

Here is a link
http://www.etrailer.com/Merchant2/me...ategory_Code=A

I have no idea what your car has, but I am surprised if it is a US market car that it has a "European" electrical connector. Maybe it is just one of the many oddball US connectors shown on etrailer.com.

If this doesn't help you, than maybe it will help someone else who is unaware of etrailer.com. I have ordered a few items from them, and was always very satisfied with them.