2006 AR 230 burning fuse on ECM box

[F1reman]

Ok I need some help!! Replaced the battery and I think my son tried to hook up wires incorrectly. No fuses burned so I thought no ham no fowl. After getting everything connected correctly took the boat out for the day. Started and ran great. After about the 4th time I started and ran the boat (all day on the water). I went to start for the last time of the day and starboard engine was dead. After looking into it I found that the 20amp fuse was burned out aft the engine on the ECM (circle cap). When I changed it out it blew again as soon as I turned the main battery switch back on (3) times so I stopped trying. Does anyone have a clue why this would be blowing and any suggestions on where to start. I followed the wires back to the battery and nothing looks chaffed. Just strange that all of a sudden after running great all day it now is burning the fuse. If it would have done that from the beginning after he incorrectly tried hooking it up it would make more sense to me. The worst part is I probably flooded the engine as we drove back to the marina nearly 10 miles and I did not know to plug off the intake line so might have a much bigger problem on my hands I just figured this out by reading a thread on here. Grrrrr. Buy a boat they said it will be fun they said. Lmao hopefully I was going slow enough and I did not flood it but I will know after work tomorrow fingers crossed. Thanks in advance for any help with the fuse. Something else I did notice that was interesting is that I have 3 black wires that connect to the battery and the wiring diagram only shows 2. In this blowout pic it shows 3 but if you look at it it actually only shows two of them with the line going through where they should be hooked up? I’m even a little confused at that.