That looks like a ground wire.I dont know what kind of wiring harness you have but i have a stand alone harness.I have a plug for the 5.3 alternator from the wiring harness that controls alternator from 5.3 computer.i also have a red wire from harness that goes to the post of alternator and i connected my red wire that went from my trucks original alternator post and connected it to my 5.3 alternator post.The old alternator wire that plugged in to the original alternator i am no longer using.