Boat owner's manuals are pretty generic, but they do have some useful info.
The boat will come with a bunch of separate manufacturer's manuals that cover the installed equipment.
Sea Ray has many of the equipment manuals on the Sea Ray website at
http://www.searay.com/Page.aspx/pageId/83090/System-and-Components-Manuals.aspx
It's amazing how little the stuff has changed in 25 years. Many times you can also go to the specific manufacturer's website and get a manual there.
The Club Sea Ray forums have a specific "Classic Cruisers" forum that discusses Sundancers made before 1989. Lots of good info there. Only problem is they've changed to this same crappy format as Iboats and the search function is just as bad.
I do have all the original manuals for my '87. The Sea Ray owner's manual covers the whole Sundancer series. I've scanned many of them into PDF files. PM me an email and I'll send them to you.
Here's a screenshot of the wiring diagram, you can see how it covers everything from the 225 to the 270.