I had trouble splicing into those trailer harness wires as well with clips (for my bed leds constant power), hard to get a good bite. I’m sure you guys know this and I’m guessing it says it earlier in this thread but it’s a million times easier to push that trailer harness “thru the bumper” vs crawling underneath and making the connections laying on your back. There are two silver clips, one on each side of the trailer harness, if you push/pinch them inward and then push the harness toward the bumper, you’ll see the clip come loose. Then you can work on the wires up at the bumper. When you’re done, put the harness back thru and just climb underneath to zip everything neat.