I wouldn't sweat it too much, as they make the wiring at the battery pretty obvious. Anything red should go on the + side of the battery and anything black should go on the - side. Most boats and accessories are good about color-coding.
Does it look anything like this ? Any cable that has red on it goes to the +terminal, and all black, or combination of black and whatever that lacks any red, goes to the -terminal. Always connect the red cables first.