I had a tail light problem that the local dealer traced to the trailer lighting circuit. The power for the trailer circuit had been spliced directly into the power to the tail lights on one side. This, they said, was a no-no with a Volvo hitch as it requires a "control module" which is then wired into the fuse box at the side of the rear storage compartment. The hitch had been installed by a Volvo dealer in another city, so if the control module story is accurate, then I got shafted by the installing dealer. I would appreciate hearing from anyone with knowledge of the technicalities of trailer hitch installation on Volvos.
Thanks, Gerry