Nice work! Glad to hear it was success. I read someone else on this forum mention a Kia parts dept referring to the harness as 12-pin and that makes it extra confusing for people just starting out.@2020 Telly,
You are correct and also very good information.
The prewired connector in the rear drivers side quarter panel is actually designed for 12 wires, but as you mentioned only 7 wires are actually wired to it and it seems to serve no other purpose than to connect to the 7 pin trailer harness. Attached is a photo of that 12 pin connector before I hooked up the 7 pin harness for anyone interested in what it looks like.
Also, I did my first tow yesterday with success. For my wired brake controller, I got a Tekonsha Prodigy P3 (not endorsing anything) and mounted that by the hood release near where my left foot rests while driving. I connected/soldered the pigtail wires that came with the P3 to the pig tail connector part AC060 and connected that to the 4 pin connector under the dash.