This may be hard or this may be easy . First thing make sure that the battery terminals are tight on the battery post and that the terminals are free from acid build up on terminals. If there is acid around the battery terminals, wash them off with clear water. The battery terminals should not be able to be turned by hand on the post, if you can twist them, then they need to be tighten. The next thing is that you have a loose connection some where on a connecting terminal, just exactly where that may be is the hard part. Sorry that i cant give you more information then this, but electrical problems are the worst. But I think the solution is a simple one once you find out where the problem is.