I'm sure every vehicle is different, but here's how it worked for me. I added a wiring kit to support towing since our van didn't come wired with a towing package. After making the connections, I laid the tow wiring kit in a recessed area under the carpet in the back of the van.
There are several rubber grommets covering holes under the carpet/floorboard in the back of our van, so I popped out one of the grommets and ran the trailer connector wire through to the underside of the tow vehicle. I leave it wire-tied to the hitch. I'm not sure how common these kind of pass-through's are, but you might want to check under your flooring in the back of your tow vehicle to see if you have anything similar that you could use.
Thanks,
Steve