I'm trying to replace my old stereo, which is the original one that came with the boat that hasn't work for years, with a new one. Now, the plug that went into the old stereo fits perfectly into the new one, but whenever I hit the switch on the dashboard for "Stereo", the fuse blows. What am I doing wrong here? Could it be the old plug, which I can replace with a new one?

Replace the plug and rewire....

Ditto. Just because the old plug fits doesn't mean it's wired the same way. Time to get out the wiring diagram for the new unit and start tracing wires from the original install. Always fun.

Thanks for the responses! It worked. I never would have thought it would be that easy...