With thr ignition "on", this charge light signifies a "difference in potential" either under/over charging. When you have proper charging taking place the light is out, when the vehicle is not properly charging the light is on. Your particular problem that is taking place could be a blown fuse, wiring problem, or alternator/regulator problem. the cheapest is to visually inspect the fuses, wiring ,etc.. If that is good, take the alternator to a rebuilder for testing and repairs. HTH!
gene