RoyB wrote:
As noted above check with ETRAILER.COM Great folks to work with...
... ETRAILER has the one that will mount inside the truck bed and then plug into in the standard 7-way connection on the bumper of the truck. You do not need to tap into any of the truck wiring doing it this way.
Looks like this setup...

This is my preference, and what I used for years. I see no need to do extra wiring.
If you tow a trailer, then you might need a "Y" or an adapter for your existing 7-pin. I am currently setting up my new-to-me truck for the TC and towing a vehicle. There are many adapters and other options.
I do not use the charging system on my truck for the TC. I have a flat 4-pin and a flat 7-pin on my truck. I will use the truck flat 7-pin for my towed (and trailers), and use the flat 4-pin with
Reese Towpower 74184 Plastic 4-Way Flat to 7-Way Round Vehicle End Adapter or
Hopkins Adapter 4-Pole to 7-Pole and 4-Pole for the TC. For my needs, I think the Hopkins has more options in the install and use.
Wayne