When you are running it and it shows 11.4v at the battery, test at the back of alternator, if it is the same you probably have a charging problem, if it shows higher voltage at alternator, you more than likely have bad connection somewhere or bad isolator. you can also check voltage at the isolator both input and output. Centre line is the input. Does you isolator have 3 posts or 4 posts?
Living the dream in the Kootenays