When recreational boats are manufactured they may buy stereos from several vendors. You get the vendor manual for the stereo when the boat is sold. Same for all of the other accessories and items on the boat. One manual does not cover all the details like it does for a car. As mentioned, get a Service Manual and/or an Operators manual for your particular drive -- it is far more valuable. You don't need a manual to tell you what the switch labeled "Lights" does. Or "Bilge Pump", etc.