It's not a grounding issue. My trailer won't light up at all with my new 2025 but every other truck I hook ir up to lights it up just fine. We tried a few other 2025's at the dealership and none of them little up my trailer. Then we tried other trucks on the lot a 2024 and all of thier sued trucks light it up just fine !! I jabe 10 marker lights and 4 taillights that are all incandescent but an that shouldn't matter. I'm told it's a problem with the software on the item and hey are supposedly working on a fix. What Frickig idiot designed something a truck to NOT ight up trailers.
What the idiots are doing when designing the software that a truck needs is each year they keep paying so many warranty repairs from customers who hook crap junk trailers to their brand new shiny pickem'-up trucks and they have tried to make the trailer tow circuits so robust to be able to handle every single style of trailer ground, light bulb and dirty resistant wiring they more than likely will have to relax the metrics in the software so that it doesn't see a hazard when the trailer tow circuits goes 1 amp over the rating.
I've been in the dealership for 25 years and I have have been around every single new year and model released since 2000 and each year their are new hurdles but with the trucks and their trailer tow circuits it can be very difficult.
What I would do is ask you to bring your trailer to the shop. The first thing I would do is take your VIN and verify that you have the correct sales code for trailer tow and then verify that all of the trailer tow equipment is installed. I believe the correct sales code is XHC. Then, I would connect the WiTech to your truck and verify wether or not the ITBM even sees your trailer or not.
This could be a very simple programming fix or it could be something that the engineers put in the software that is not allowing the ITBM to see the trailer.