Some can and some wont charge at all. I would check the wiring and then unhook the field wire to the PCM to see if it stops charging. On most of them the PCM just ground and ungrounds the field to control output. If it stops charging with the field unhooked then it sounds like the PCM but also make sure the field wire from the alt to the PCM is not grounded as that will make it overcharge. If it still overcharges with the field wire at the alt unhooked then it sounds like an internal alt problem. A grounded brush could also keep it overcharging. And as was said you can wire in an external regulator as I have done that for a few people who did not want to buy and alt. You just run the field ground wire to the ext regulator and also wire 12 volts at key on to the ext regulator to do it that way if its in the PCM. Ron