I own a 21.5' Spectrum sail boat I
The best source (I know) for boat how-to's is Bluewater books, in FL. They have an excellent well informed staff and take the time to help no matter how big or small your potential purchase. Nigel Calder has a cpl. very useful books.
any of the books by Nigel Calder will give you the details on proper marine wiring. I suspect your boat was made in the 1970's or 80's and the wiring is not adequate for today's safety standards. The number of fuses depends on the accessories you have. And you want to be sure to fuse each major accessory e.g. bilge on one, radio on one, navigation lights on one,
