You know the battery fuse is ok because the battery powers the 12v things. so the open is not that. You want to know if the converter 13.7v is reaching the DC fuse panel so it can run the 12v stuff. Should see 13.7 at the individual fuses at the panel.
If only 12.x (battery voltage) at the panel, then the open is in the converter to DC panel which is also where the converter to battery goes.
The battery lugs and the converter connections to the DC meet there. You could have the battery wires on their lugs but one of the converter wires not in its lug.