Thats crazy... That highlander most likely has the harness already installed. Just need the hitch.. Dont know what else comes with the tow package on that truck...
Anyways for 175$ you can get a hitch... The truck only can tow 5000 so this is over kill..
I wouldnt waste money on the factory hitch..
You can install this yourself in probably 30 minutes.. Then go to a trailer place and get the 7 way installed if needed. But you probably have a plug and play..
Brake controller if you get one is plug and play too most likely..
http://www.etrailer.com/Trailer-Hitch/Toyota/Highlander/2017/C13200.html?vehicleid=201729871