You might have corrosion built up inside one or the other of the cables. I'm thinking that maybe where the ground cable connects to the body that you might need to clean that point.
After trouble shooting and fixing any problems go to the autoparts store and get a plastic tray for the battery. It just sits on top of the stock steel tray. Plastic dosent corrode from battery acid. Good luck!
Unbolt the tray, scrape it clean with a wire brush, use rust dissolver if need, spray rustoleum primer and repaint, that's what I did.. I can send you pics.
Hey Thanks For the reply . I actually did all that , the only thing I did different was apply dupli color bed coating to the tray and to the fender well area , turned out nice , so for so good.