A ground is not going to have anything to do with it backing up or lights plugged in since it has surge brakes.
Brake fluid level does not matter.Most surge brakes with disc brakes will lock on backing up if the brake fluid is low.
I have a 2004 Ski Centurion trailer that locks up whenever I try and back up. I have done some reading on this but I can't get them to work. I have some pictures. Thank you in advance.