Urgently Need Help Diagnosing Dead Electrical System

Those little auto reset breakers can go bad. Check continuity with a ohm meter. or check volts with a vom . one lead to ground and other to either side of "Shortstop" should be volts to ground on both sides. Your convertor may have an internal fuse you don"t see. If nothing at shortstop go into the convertor. Mine has a glass fuse on both the 120 side and 12 volt side.