V70XC Trailer lighting

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

 

Yes, a "control module" is needed. At least it was on the three
Volvo's I had trailer hitches put on.

 

I have a '01 XC70 with a trailer hitch. I wired the hitch my self and
it works just fine. I had to get a module that converts from the Volvo
system with 2 yellow turn signal lights and 3 red brake lights to the
standard trailer hookup with two red lights that are both turn signals
and brakes. I got the module from U-haul. That is what my Volvo dealer
recommended. It works great. My dealer also recommend the U-haul
trailer hitch which was especially made for the XC70. It also is great.