@TRAMPER (or anyone with a '23) to the red phone. We need images of the wires going into the black connector from a 2023. There is a chance that various pickup trims have different wiring, but I think all pickups have tailgate ajar warning for when a tailgate is left down, don't they? If so, your '23 tailgate removal harness, which actually work, will likely have wires/pins in 2 and 3, which I suspect are the right and left tailgate clamp sensors. I suspect the tech that did the below work determined port 5 had good ground so he pinned that as an easy way to feed ground into ports 2 and 3.
From the various descriptions, it seems that the right and left tailgate clamps individually know if they are closed or not and the full closure grounds them, hence, if both of those wires, leading back to the computer are grounded, then computer interprets that as the clamps being closed. The tailgate removal harness should be doing that, but the '24 batch is missing pins/wires to ground those two ports all the time. This is all theory and I don't know which two of the three ports are actually the right and left tailgate clamps wires; could be 2/3, 2/5 or 3/5. The other is simply a convenient source of ground to feed ground to those other two.
So, would really like to see a '23 harness. Owner doesn't need to remove from the truck; just some clear pics of the plug so we can see all the wires going onto the top 6 and bottom 6 ports. When you post, please indicate it's a '23 (so everyone keeps that clear) and also indicate your trim level. Thanks in advance!
Edit: I'm editing to note that further down this thread, we discuss and discover the official pin position numbers for these location.
They are positions 14, 13 and 11. Reference updated image in post
https://www.fordtremor.com/threads/24-owners-who-removed-tailgate.18096/post-404316.