It is impossible to know the state of the wiring in your boat. I would think a boat of that era, unless a prior owner rewired it, would be something of a mess.
I bought my 71 Ericson 29 a few years ago knowing at the time the wiring was in bad shape. The panel was a rats nest of confused wires and old, gooey electrical tape. I wanted to install some new gear and had no idea where to hook it in.
I decided this year to rip everything out and start new. All of the old wiring was removed and will be replaced with true multi strand tinned marine wire. New breaker distribution panel, bus bars, etc. The hardest part has been going through all the books and figuring out the wiring diagram. I had originally foolishly thought I could do it without but realized there was no way. The only way to do this is with a clear plan on how to rewire it. This is the only way to know what wire and other parts you will need. Doing this gave me a chance to make sure everything was fused correctly.
I am at the rebuild phase now which I will work on over the winter. Good cold weather job since no epoxy or paint to cure.
You will regret the things you did not do, more than the things you did.
Get out there!
Saco Bay, Maine
1971 Ericson 29