Usually speaking if the tow vehicle only has a 4-way type connection is wasn't a big enough truck to tow a very large trailer - maybe something like the small utility trailers... These same tow vehicles also usually only have the one-inch size trailer hitch setup as well
I always got all of my trailer wiring info from the ETRAILER.com site. Guess they still have all of that info available along with lots of how to videos...
My two most recent FORD trucks had the 4-way/7-way Combo Trailer connector installed... Pretty neat having both connectors to use..
If I was changing a 4-way over to a 7-way I would install this combo connector setup...

Moderator notified to resize the very large photo from the OP here... Sure creates a big mess trying to view and make comments when one that large is being used. Most of my general info photos use the 300 setting and then I like to use the 400 setting for large view of something. I think the max the RV NET management likes to see is the 600 size... It was like moving my screen over to the next county here to get to the links to make comments hehe...
Roy Ken