Ok im puzzled on my friends xb. 2008 gen 2 xb. Alternator is not charging the battery. Battery voltage is good. Slowly drops cause the Alternator is not charging it. I replaced Alternator and it still did the same thing. Took both Alternators in and have tested. both tested good. I checked fuse and its good. Does anyone have any wire diagrams for the charging system? There is 4 wires that goes into the Alternator . 3 of them read some voltage from the battery. One wire 8-10 volts. The ground wire are good. Ground from teh battery is good. No problems starting just no charging.

 

After all of that, still sounds like a grounding issue. Go back and really double check that. Otherwise, you've definitely crossed wires somewhere. Those are the only things it could be.