Altnator is good but not charging
Use multi meter to check alternator output voltage. Should be 14.5 or so volts. With vehicle running place one lead of meter on large wire on alternator and one lead on metal of the motor. If you have the voltage then place one lead on positive of battery and the other on metal of motor. Still have voltage? If so then place one lead on positive and the other on negative of the battery. Still have voltage? If so then clean and tighten your battery terminals. If not then clean and tighten the negative battery cable where it connects to the frame and motor.