I started this conversation off-line but I thought I'd take it to a larger venue.
Prior to my paint job and power transfer switch installation, I always plugged in my Argosy to a GFI outlet on the back of my house to keep the battery charged and the vent going as needed. When I returned from Florida, I plugged it in and the GFI popped. I suspected the automatic transfer switch but when I rewired the coach directly to the GFI (bypassed the switch), it still popped the GFI.
I then went to the main panel and disconnected the neutral wires. When circuits 2 and 3 are wired, everything works with the GFI. When I connect the #1 neutral, even with the breaker off, it pops the GFI.
Circuit 1 powers three outlets including the old Univolt (TU-440-6 Converter Charger). I still get the fault when I unplug the Univolt (which uses a three-prong plug). I did try plugging the Univolt into to a cord with a GFI and it does not pop the GFI. For some reason, the voltage on the 12v
panel is running 18 volts though. Normally my readings are 12-13 volts. Ideally I'll replace the aging Univolt but it looks nearly impossible to remove in it's current location.
The three outlets are the old mobile home outlets that actually use a continuous wire through the box. It's kinda hard to troubleshoot those old boxes. I guess I am going to have to pull out the boxes and replace them with more modern ones in order to troubleshoot.
If I plug the unit in to an outlet without the GFI, everything works fine. What concerns me is that there is a fault somewhere and I'd like to get it fixed instead of getting electrocuted one day!