Re: Towing wiring Harness Hook-up
It's under the passenger-side rear fenderwell. I just finished adding a towing package to my Acadia with the information on this site and the Acadiaforum.net site.
You will need to have the fuse-block replaced if you want to use the factory wiring harness, though. For 2007 model lambdas GM did this under warranty. For all later versions it costs around $350 to have it done at the dealer.
The hitch, bolts, plug, and harness are all available at GM PartsDirect for a pretty fair price (I think it's around $220 all in). It all goes on easily. It took me about 25 minutes to install the factory hitch and wiring harness.
You can get an aftermarket package with a electronic modulator for less than half of what all of this costs, but I wanted the factory system. I had a few issues with GM over this vehicle and fought with them long enough to get reimbursed for most of what is listed above. In the end, they were pretty fair.