Over the years, I have made it a practice to unplug the camper from the truck, EVEN if I have an isolator. I had one short out a long time ago. I just got into the habit of unplugging the 7 wire from the truck and sticking it in the gas/fuel filler cap. That way when I jump in the driver's seat, I can see it stuck in the gas door.
Like Sleepy said, by disconnecting the camper from the truck, it will cut the diagnosis in half.
And if I missed it, the only other thing is to check the condition of the batteries. I have had an occasion where the camper battery was shorted out and would wear down the truck battery if I did not disconnect the camper from the truck.
