To put it another way…your boat is 36 years old. Chances are very good that at least one if not more shade tree Bubba’s uttered “hold my beer” while “fixing” an electrical problem. So even if such a diagram existed, chances are really low that it still pertains to your boat.
Best advice is to crawl under the console and start tracing wires. Document as you go.
FWIW…my ‘83 Blue Fin has at least (2) Bubba’s worth of “fixes” which is why I’m ripping everything out and rewiring it myself.