I have a 40 hp mercury outboard that is blowing 15 amp fuses. When I replace the fuse the engine runs and every thing seems fine. I can turn engine off and start it up again right away and it works. However if I try to start engine or use trim the next day, it doesn't work because fuse is blown again. I noticed the positive cable from the battery to the engine was damaged in a couple of places and there were exposed wire spots which I taped up. Also the manual says to use 20 amp fuses but my fuse holder had three 20 amp fuses and one 15 amp fuse, not sure if this correct also. Any ideas?