Hmmm, this fuse holder appears to be for a High Current (as in 30 Amps or greater) Large Blade Style Maxi Fuse and definitely looks after factory to me. Did you purchase the FF used? Can you chase down where the other end of the fuse connects? It could be used for any large load or perhaps in series with portable solar panels.
2016 F281BIKS, Added Renogy DC-DC charger to better charge deep cycle batteries.
2003 F250 7.3L Powerstroke Crewcab longbed 20K lbs GCWR