You can find most original schematics online. Problem is that used boats are notorious for having wires corroding and new wires replacing them. My point is that almost every boats wiring is changed from the original in someway, and there's really no way of telling what wires you have in your boat. I've found that the easiest thing to do is rewire everything, using common sense as the basic blueprint. (Understand, I'm talking about add on equipment, not your engines wire harness).
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1987 V20 w/1987 150HP Yamaha on a Shoreland'r Trailer
1978 16.5 Airslot w/1996 120HP Force on a Four Winns trailer
1996 V21 w/1993 200HP Mercury on a Shoreline Trailer
All towed by a 5.7L Hemi Durango.
If God didn't have a purpose for us we wouldn't be here, so
Live simply, Love generously, Care deeply, Speak kindly.
(Leave the rest to God) 
Silence, in the face of evil, is itself evil. Not to speak is to speak, not to act is to act. God will not hold us guiltless.
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