NOT normal, there is a 30a (40a? varies w/ model) MAIN FUSE between CONVERTER AND FUSE PANEL. The Other MAIN FUSE is between battery/ fuse panel, but sounds like that one is good? (Often labeled "REVERSE POLARITY). There is also a 120vac Breaker Feeding the CONVERTER? SOME BRANDS of Converter may have a RESET button? Someone may have put battery backwards, and blown both fuses, but only replaced the one? EDIT: You DO want Battery Switch=ON when plugged in so that Battery is charged/ charging. TIP: Charged battery will NOT Freeze, DEAD battery will freeze/ break.
2000 Conquest LE 6266, Class-C on 99-E450SD, 6.8, 2v, V-10