Re: Head Question
That sounds like a vacu-flush head. I'd be more concerned with why the head is running, although certainly disabling is a good workaround until that can be done. I suspect there is probably not a breaker on the panel dedicated to the head. You could theoretically, find the lead to the pump and install a switch to turn the pump off, but I would check to see if the pump has a switch on it first. the pump should be near the holding tank.
I believe that the pump is uses a pressure switch, similar to the pressure water system. When the head is actuated with the lever it opens a valve causing pressure in the sanitation line from the head to the holding tank to drop, turning the pump on. I believe there is a 'ciruit' (water/waste not electric) from the water tank to the head, then back to the holding tank, so when the pump is actuated, water is sent from the water tank to the head, then back to the holding tank. If the head is 'running', then it sounds like there is a leak in the vaccum. I would suspect it is the valve that is on the head itself which is actuated by the foot lever.
Is the holding tank slowly filling with water as time goes by? If that is the case, then the vaccuum leak would most likely be between the head and holding tank. If you're not smelling holding tank odors in your boat, then the valve at the head would be the most likely culprit. If your water tank levels are going down, but the holding tank isn't filling it might be a leak in the fresh water feed. If that were the case, I'd expect you'd see water where the leak is occuring and find water in the bilge after some time.
Just some thoughts. Someone may have a better opinion than I.