Late to the party and I need to make a full trailer write-up within the next few days.
But, I may be able to help you.
Our new unit has 2 batt disconnects. The driver side batt box ground wire was reversed with the second batt disc switch. The black wire leading to nowhere was bolted to the trailer. But, the primary trailer ground from underbelly was taped up and zip tied with the other loose conx.
In other words, everything downstream of the bat disc switch 2 (inverter for fridge, battery charger, etc) was not powered by the vehicle or ship battery. Only time (residential all electric fridge) worked was on shore power.
Solution: Opened driver battery door and bolted both ground wires to the frame. Like magic, everything came to life.
Chevy 3500HD Dually
XLR Thunderbolt 417amp
RZR XP 4 1000