[jclark003]

It would help to identify what boat you have. Also what 12v circuits/breakers are affected. Presumably you are describing the circuits assigned to the house battery bank. If so and you are comfortable working around electrical circuits, first thing I would do is check the house battery bank connections and grounding.

Breakers and battery disconnect switches do go bad from time to time. It’s really just a process of working backwards from the cabin panel until you find volts or forward from battery bank until you have no volts. House Power typically runs from house battery bank to disconnect switch, to cabin breaker and or helm breakers. Some boats have multiple main breakers with one in engine room (ie cabin main) and another at the cabin distribution panel. To test breakers or disconnect switches use your test meter to check for 12V on both terminals with breaker closed (on). No volts on either terminal means the problem is down stream towards the battery bank, 12v one one terminal means a bad breaker, and 12V on both terminals means the breaker is working and problem is up stream towards the panel.

Hope this helps.