If you have a multimeter, or a test light, check for voltage at various points. I think your MH is the same as mine. The wire from the battery, in mine, runs from the battery to a circuit breaker under the bed, then to the battery disconnect solenoid then to the converter and the fuse block. The wiring under the bed is in a compartment on the passenger side, under the bed.
You did check the battery disconnect switch by the door?
Check that 12v power is present at each of the above points.
When not plugged in to 120vac power the converter is not in the circuit so it is unlikely to be the problem. However, the wiring in the area could be.
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