Yeah, so, the one thing I can't really seem to find the solid answer to... is, exactly how can you connect a controller inside the cabin of a 2021, which would make full use of the Kia OEM 7-pin wiring.I'm in exactly the same situation except I have a 2020 FWD S. But my needs are identical. I just have a slightly more complicated path to get the 7-pin on the back than you. I guess my pain is your gain.Don't forget though, if you borrow someone else's trailer you still need a brake controller. The e-brakes on the trailer won't work without one. I think that's one of the points that Kia and dealers are missing to point that out to buyers new to towing.
One would think that if they have wires that connect the 7-pin right into factory wiring, that there would be some way to wire a controller inside the cabin, without having to drill holes in the firewall, etc... So far, I haven't found a answer to this, other than the 'wireless' aftermarket things, but that seemingly defeats the propose of having 7-pins on the trailer harness directly connected into the main vehicle wiring.