The reverse sensors think you're backing into an object because you disconnected the trailer wiring harness..just need to reverse slower or plug it back in.
This is great and glad to see gathering interest! I've tried a few times via FB to do this around Barrie area but no luck. I'm very interested myself in coming and joining the convoy from the GTA.
For those that are not aware of the club, here is the link for Ontario F-150 Lightning BEV Owners...
But again, it's not the size or mass of the trailer that cuts the range in half. Its the shape/drag created by the trailer. I have a 1k lb open utility trailer that cuts my range in half. But I don't have to go far so it's never an issue for my Lightning.