I ran into a strange happening a couple years ago. I had won one of those AC line test meters which I plugged into an outlet in the motorhome. All was well...until one evening, the buzzer went off indicating an open ground. Long story short, another rv pulled into a site 2 away from me during the late evening. Once he plugged in, the open ground appeared! I know this because three days later when he left the problem once again went away.
On a side note, I built one of those testers that allows you to test the pedestal for voltage, shorts, open neutral, open ground etc etc. When he was not attached to the pedestal, all checked out and when he left, I checked that pedestal too....all OK. When someone else pulled into that site and plugged in, no problem once again. The moral of the story, sometimes issues can be your own, sometimes it can be the campground and sure enough, sometimes it can be someone else's issue causing your problem. Just found it interesting that another person's rig could cause issues with ours knowing that pedestals are looped together in many different ways.????
96 Vogue Prima Vista
The Kid's: Humphrie, the Mini Schnauzer and Georgie,wire haired dachshund.
Rainbow Bridge: Laddie,Scoutie,Katie,Cooper,Kodie,Rubie,Maggie, Cassie, Mollie, Elvis, Potter and Rosie Love You! (40+ years in all)