Volvo 780 bunk control says err

my Volvo is having some issues with bunk control/low voltage disconect. I have no lights or power outlets in the truck. Intermittently I can get the from half of the truck to turn on the overhead lights and cb but nothing in the bunk. Put a new low voltage relay in the fuse panel checked all fuses under dash and the fuses in the bunk. Batteries are at 13.8 (new last month). I did get the rear panel to show err in the digital display for a bit but you could hardly see the digitial display it was that faint. Does anyone know what the err would mean I can't find anything on the bunk control where it tells you what that means. The truck is a 07 780.