Question About Installing Stereo

[toondog]

You may just want to ignore the mess of wires. If you have a stereo switch like lakerunner, connect the red to the switched side and the yellow to the hot side of the switch. Lakerunner connected both to the switched side because he didn't care about memory. The memory wire will drain your battery if you don't use your boat for a long time.
Then I would run your black wire (ground) directly to the fuse box where you should have a common ground.