Extra wire at alternator could it be a ground wire if so where does it go?

I believe on most alt. you have a positive hot (red) wire that usually goes to the threaded bolt on the back of the alt. and goes directly to the positive terminal on the batt. and a ground wire that goes to the frame of the alt. usually you put it between the frame of the alt. and where one of the brackets bolt up to support the alt. just pinch it between the two and run the bolt through the mounting bracket and the wire and the alt. and tighten it up and that will ground it. then you will have a plug and wiring harness that just plugs into the alt.