20 AMP fuse blows as soon as the battery is connected

[attorneystone]

I have a 90 hp Mercury. It has had no issues the last two years and ran perfect when I put it away for the winter. This year when I connected the battery, the started engaged itself on its own (key not on) and then stopped. Then I noticed smoke coming from under the dash board. All other components of the boat work. But the fuse blows almost immediately when the battery is connected. There is a pretty good arch when I connect the negative terminal and then pop! Thoughts?

 

[Silvertip]

Reversed the battery cables when you put the battery in didn't you!

 

[Mi duckdown]

That's my guess also

 

[attorneystone]

20 Amp Fuse blows when I try to crank the engine

I will admit it. I am a dummy for getting myself into this one. I was connecting the battery on my boat and accidentally connected the ground wire to the positive post with the positive cable. I fried the ground wire from where the harness connects to the engine all the way to the ignition switch. I ran a new wire. Someone suggested to disconnect the regulator and see if the 20 amp fuse would still blow. When I went to disconnect the regulator, the rubber covers at the connections were all stuck together from getting too hot. So I replaced the regulator thinking it was fried as well. Now atleast I can turn the key to on and the gauges will work as well as the choke. As soon as I try to start the motor the fuse blows. What else am I missing?