help charging problem 87 gt

[brad87]

I need help with charging system please the deal is I went to start the car and the battery was dead after I just drove it 30 min before that I have no volts reading 8 but not charging.heres the weird part I changed the alt.and doing the same thing when I unplug the alt. plug (either one) the alt. spins freely when I plug the plug back in it kinda locks the alt. and it does not move freely and gets hot any ideas thanks.