I just installed the Curt hitch and wiring harness. I don't know about the Amazon harness, but the one I bought plugged in on the passenger side of the car, on the side of the trunk compartment. It's pretty easy to do, just takes about 30 minutes. For the record I don't have the towing package, from what I read all current CX-9's have the wiring in the car, mine did and it plugged right in.
This link is to a youtube video of the install. https://www.youtube.com/watch?v=DdHgr0-P6vU
Not sure if this applies to the pre-2016 model though.
This link is to a youtube video of the install. https://www.youtube.com/watch?v=DdHgr0-P6vU
Not sure if this applies to the pre-2016 model though.