it's almost certainly the ground wires that are atttached to the inner fenders near the top and just behind where the battery and air cleaner are. you need to remove ground plate w/ a 10 mm socket and clean it as well as where it mounts. Also, there is a spade terminal on it that should be cleaned too (i.e., get tout he file or the sandpaper. That should cure your problem like magic. (this from experience).