I just had the same problem, and thanks to info I got from this forum I was able to fix it. If your battery checks out as mine did you might look for a breaker box that on the main feed. Its only bout an inch x 3/4inch rectangle and the primaries from the battery hook up to it. Apparently the newer ones are designed to automically reset but the older ones have a manual reset. Can check it with a meter to see if it is the the problem. Only costs a few bucks to replace and easy job. Had 4 other RVs and never even knew about this thing that apparently is on most RVs. If its tripped you will only have 12v when you have shore power connected.