I wouldn't use the circuit breaker as a switch. That's a sure way to get it to fail early.
If you aren't hooked up to shore power, and you have 12 V lights working, then the converter is working. Among other things, check the battery connections to make sure they're tight, and check the water level in the batteries. If you have a battery hydrometer, use it to check each cell, too.
Check the converter to see what make and model it is, and if it has the ability to do a three stage charge. The Iota converter of that vintage has an small external plugin that gives it the three stage capability. If it doesn't have it, and they are the original batteries, there's a good chance that the batteries are bad. If the converter is an Iota, you can get the plugin for about $30, and it's well worth it. The two stage charger has a tendency to overcharge the batteries, boiling off the water and shortening their lives.
I second JP's suggestion to check the wiring to the converter, and, while you're at it, make sure all the wiring connections at the power center are tight, especially the grounds.