I dont know if this is your problem or not, but its a start. I was having intermittent gauge problems the weekend before last. My issue was a loose connection on the computer under the dash, I think it is the DECC or something like that. if you look the front wall under the dash you should see a box mounted to the wall, there are a bunch of screw in connectors and two studs, one stud is the negative and the other is positive for the computer. Check the positive and negative studs to make sure they are tight. On my boat, I actually had to remove the wire ring from the stud and add an extra nut as a spaced because the ring termial was mashed inside the plastic housing and the retaining nut would not tighten down allowing the wire to intermitently loose contact.
Im not sure if that make since or not, if I remember when I get home tonight Ill take a picture of what I am talking about.
