Run through your trailer wires everywhere it goes through the frame or some other metal. Make sure that the wires running from each side of the brakes are clear of any nicks. I have seen a wire in the middle of the axle have a small nick in it causing all kinds of issues. We tend to drag axles over things and if the wires aren't tucked up properly, they can get nicked up. Remove all the trailer grounds and clean them up real good. Verify that the wiring to your trailer battery is all good and connected properly. The truck powers that when connected but if disconnected, the batter powers it but if it isn't connected properly then it can cause a fault.
I know some of these things would usually pop a fuse but I have seen crazier things.
That's a good spot to check. Take it apart and hit it with some electrical parts cleaner and then dielectric grease.One of my super duties had a ton of corrosion on the back side of the plug on the truck. The actual plug is two pieces. The harness side plugs into the back of the plug body, that is where the corrosion was.