The Curt T-connector works perfect on my 2016 Nissan Frontier. I just cleaned the plug under the drivers side near the back of the box (underneath) and plugged this Curt connector in. It fit properly, and when hooking up the utility trailer, all the lights worked. A really good buy, and saved me time otherwise having to tap into existing wiring.
It turns out it wasn't the wiring harness that was the problem. Nissan had a recall on the trailer lights years ago. The fix included installing a set of fuses under the dash above the accelerator pedal which they never informed anyone. The left side lights were not working because the newly installed left side fuse was blown.