Some time ago I found out my front headlights were not working. After checking out a few things I noticed I had 2 black wires down by the alternator without a home. In the pic below the alternator posts are labled 1 to 5. Am I missing a post on my OEM alternator #5 ? If so, I suspect that is where my 2 black wires attach.
If I remember correctly, they are both ground wires, one coming from the voltage regulator, and another coming from the EGR valve sensor. Trace them out. Even though this is the new alternator you should be able to see the two black wires attached to the frame.