I don't know much about your boat, but if the manufacturer is still in business, they may have wiring
Break the systems into individual systems and look for manuals
Most boats like yours (I have seen) have Detroit 671TI engines. There's a lot of info on the web on Detroits. I have 671s, but a different model. Ebay is a good place to look for manuals
. Other Viking owners may have manuals, diagrams you could have copied.
When I buy a new-to-me boat, I trace all the plumbing
and main wiring
. In an emergency
, it's nice to know what to shut off and where to do it.
If you do have Detroits and have questions, I've used them a long time and do my own overhauls. My favorite diesel
and very reliable.