The fuse was the 300 amp fuse (as in your picture), I have 2 group 31 wet cell batteries with minimal electrics on the boat (sailing instruments and vhf, water pressure and cabin lights), yanmar 3gm30F and no I have not continuity tested the fuses which I will do shortly and get back to you. I have a Charles 50 amp charger from the late 90s and the simple 1-2-off Both switchGoing to need some more info on this one... Fuse size, load size, engine starting etc.? Have you continuity tested the fuse?