Good Luck. Most boat manufacturers in that era simply ran wire wherever they needed it and didn't bother with diagrams. I can provide a drawing of a generic instrument panel if that would help you.
hate to tell you, but it's chase the wire. turn on the switch, and see if you have power. there are alot of how to books out there, that can help you. what i usually do, with a rehab boat, is strip it and start over.