I will go out on a very short limb, and guess that it's extremely unlikely such a thing exists in any official capacity.
A generic boat wire diagram may be of help to you, and actually be possible to find. How many electrical components could such a boat even have anyway? I know my '72 Starcraft had a something like; the bilge pump, running lights, and the ignition switch...
Welcome to iBoats. Highly doughtful you will find anything boat specific. Folks here are very willing to help if they have some idea what the issue is. Might suggest being a little more explanatory as to what you are working on. You didn't mention what type motor!? Outboard - I/O - inboard? Are you replacing all the wiring or just trouble shooting a problem? There really isn't much to a boat of that vintage as far as wiring goes.