alternator not charging battery

[celica92gt]

Hey guys I'm just a backyard mechanic and I need ya'lls help. I have a 92 celica gt. I replaced the alternator about a year ago and the battery. I had a bad connection on it the whole time and I just dealt with it. Now I have replaced my battery and alternator again because the bad connection actualy burned up the wires and the connector on the alternator post.So I when down to lowes and bought a lug and 4 gauge wire. I wired the wire from my harness into the lug and the 4 gauge wire together. i then put a eyelet connector made copper on my alternator post. The eyelet is a litte bigger but still seems to make contact. I'm not quite sure how to test it because I dont have proper wiring diagram. And that would be the only way I would know how.But I did test from the post of the alternator to the negitive sized of my alternator. My voltage on my meter when from 12.5 vdc to 5.6 vdc. Could I have rectifier or diode problem? Please help.Thank you in advance