My 77 Sovereign
also does not have an isolator switch... at least none that I have ever found. I had issues with my panel having burnt connections, wires hanging, and melted fuse holders. I rebuilt the panel completely with 2 new fuse blocks and 2 heavy duty 50 amp LED fuse blocks that they use in high end auto audio systems. Now every circuit is working perfectly. Even my antiquated Airstream control panel is all lit up. Prior to me changing out the panel, things only worked sporadically.
I also picked up an intelligent charge controller for the Iota 55 amp converter. Now all systems are a go.