Is there a truly off-the-wall-chance that the converter feeds the batteries then has a separate line to the fuse distribution? i.e. Disconnected battery cables, separation of converter and feeder line to fuses? Until a power-loop interconnect failed?
Too many of these types of posts ask for help but the poster neglects to say...
a) Whether they have a meter or test light
b) If they are knowledgeable about how to use either one
"Gee, my back hurts. Can you give me explicit instructions to make it not hurt?"
Some investment in time, effort and money is needed by a rig owner going into these diagnostics or I get the impression that an individual believes in miracles...or magic...