[Bob Landry]

This is a confusing thread and that's compounded by the OP's lack of understanding of the electrical system in the trailer. The first thing is to understand the difference between AC & DC and what runs on each. The AC power distribution works the same as in a stick house. The AC panel gets power and distributes it throughout the individual circuit breakers. If anything works, the AC power is good. The converter is also powered from an AC circuit breaker and provides 12V as well as charging the battery. With the battery turned off/disconnected, everything else is powered from the converter. if the lights flicker or dim with the battery turned off, the converter is bad. If you disconnect from shore power, the battery should run the lights at a stead brilliance.
An open ground, indicated by the EMS, while a potential safety hazard, will not keep any of the AC appliances from working. It will also not keep DC devices from working because the DC ground comes from the negative side of the battery and the frame of the trailer.
People have a tendency to ask a lot of irrelevant questions when these electrical issues pop up, but troubleshooting a trailer's electrical system isn't rocket science. and a little understanding about how everything works, goes a long way.