79 Carver Voyager 28, 2 battery system. Everything works fine on shore power but when I disconnect, the interior lights and receptacles don’t work with selector on either batteries. The boat engine and fly bridge controls/panels do get power and engine starts. The boat is in fact new to me, did I wire the batteries wrong or am I making some silly mistake here? Or is that normal, I doubt it? Kind of stumped because they do work on shore power. I’m normally quite a skilled mechanic but this is my first boat with a house cabin and the electronic for such are a little alien to me.