Do you have alot of extra lights or a high poered stereo with an amp? If so, does the amp have a good sized capacitor, because if you don't it will over load your alt. and kill it. If you have some off road lights, do they have relays on them. It sounds like there is an overload on your system. The other thing to try is check ALL your ground connections, There might me one that is loose that could cause your problem, especially the one that goes from the body to the engine, or frame to engine.