Electrical problem

My boat has a 12 v. system with 24 circuit breakers. A problem has suddenly popped up in which turning on one CB sends power not only to its own circuit but 8 to 13 v. to five other circuits. The 18 other circuits all work normally. Of these six circuits, turning on any one causes volts to appear even though the other five are "off". None of the users of these circuits actually work. They get volts but no amps. The users are a water pump, radar, electronics, and autopilot. Last week my regulator failed and in the over charge burned out a 2/0 wire and fried two radios. Replacement of the 2/0 wire restored most of the system until a week later when these six circuits started acting strange. The red (+) can be totally disconnected but still show volts if one on the other five is turned on. It's a 12 volt system. Hopefully someone out there has an idea.