2013 Traverse - Dead wire for right lights on 4 harness trailer

I have a 2013 Traverse LT AWD (97K miles) with no factory tow package. I ordered a U-Haul class 3 tow package through their website and installed it without problems other than piss poor wielding that prevented U-Haul's own receiver hitch from fitting it. I went to U-Haul's hitch department and the guy who worked there confirmed it happens to him too sometimes when he installs their own kits for customers. He told me to buy a metal filer and just file away, and then spray paint it. I got it fixed that way. Anyways, just wanted to point that out for the record to help others.

The real issue for this post is I bought this item below from Amazon because it was recommended to fit my Traverse by U-Haul:

1. CURT 56245 Vehicle-Side Custom 4-Pin Trailer Wiring Harness, Fits Select Chevrolet Traverse, GMC Acadia, Buick Enclave. When I inserted this item into the trailer wiring component provided from the factory by Chevy on the side on the car by the muffler, it clicked and fit perfectly. I didn't test anything and assumed it'll work. When I hooked up the 4 wire harness from Curt to the 4 wire harness from a brand new enclosed trailer at the store, the trailer lights either ALL didn't work or flickered, depending on what we were doing, especially when I drove, even at 1 mph or less. Bottom line, it looked like a grounding issue. The trailer company used a device to test their wiring and the trailer lights worked fine.

So I went home without purchasing the trailer and bought a circuit tester and verified by getting under the SUV and wiggling the connection point between the component from Chevy and the Curt 56245 piece that connects to it. The light from the first wire next to the ground wire flickered as I continued to touch the wires as well as turned off completely (when using the ground wire as a test). I couldn't tell if it's the wiring from Chevy, wiring from the Curt component or the connection between the two were faulty. When testing the SUV frame as ground, it worked without flickering. I then spliced the ground wire from the Curt component and ran it to the Traverse frame. The wire next to the ground (which represents all lights) was now solid. I tested the left turn signal (2nd wire from the ground wire) and it flashed with the turn signal. So far so good. I can't remember if the right turn signal wire (furthest from the ground wire) worked or not. I thought I tested it, but I can't be sure now. When testing with the trailer, the last wire didn't work so the right light used for right turns and braking didn't work. The left side works. I already checked all fuses and swapped the relays too. I went home without the trailer again...

Now I have the fun of testing the last wire and trying to find where exactly the break in the line is. The problem is I don't know how to disconnect the Curt component from the Chevy factory component because it's so tight I can't even see anything. I might have to take the back bumper off to access the area where both pieces connect, but I don't know how to.

2. CURT 58300 Vehicle-Side Trailer Wiring Harness Mounting Bracket for 4-Way Flat. Note, the CURT 56245 item didn't fit this harness. I had to file the plastic raised edges of the 4 pin harness to make it fit this item. Pretty lame. Just FYI in case it helps someone.

Any thoughts guys? Are there known issues with the 2013 Traverse for having connection issues with the problem being Chevy's poor design, or a known problem with Curt's design? Anyone know how to take off the back bumper? Thanks in advance!