I assume that since you mention your 1999 Boston Whaler 230 OUTRAGE has a diagram showing two batteries and two switches that the boat was rigged with twin engines. Please mention how many engines the boat has now.
The usual two-battery two-engine wiring for Boston Whaler is described in an old article I wrote years ago in REFERENCE. See
http://continuouswave.com/whaler/refere ... ttery.htmlYou can also ask Boston Whaler customer service for a wiring diagram. And try
http://whalerparts.com to see if a wiring diagram is posted there.
If someone has been tinkering with the boat's electrical wiring--which is very common and must have occurred in your case--you should not expect that an original wiring diagram would describe the present wiring on your boat. Previous owners and dealers often add (or subtract) electrical wiring and circuits from boats. And often in a manner that is not particularly well done or attractive.