Jim, not sure you have a fuse panel thru a access panel on your dash, its clearly marked on panel or you have a fuse panel in compartment on drivers side outside. The fuse panels were always clearly marked for fuse for steps.
Sometimes the magnetic switch on door jam for screen is defective give it a wack with handle of screwdriver may free it up. Also the ckt works thru your brake switch and may need adjustment.
Brake switch adjustment