New 200 amp alternator not working

I just got a 200 amp alternator for my 2002 s10 pickup, the guy I bought it from said I need a new plug to make it work. So I got that plug. The factory plug has two wires that are the same size a red wire and a gray wire. The new plug has four wire 2 brown wires and a gray which are all the same size, and then there is also a red wire that is a little bigger. I guy I bought it from told me I only needed to hook up the gray wire from my factory to plug to one of the brown wires on my new plug. This didnt make much sense to me, and the alternator is not charging the battery so I am guessing this is why. I need to know what to try next. Also what do the wires in the plug do? Do they tell the alternator to charge the battery or something?

I would take it in to a shop to test it and make sure it works.. HOw would this guy know that the plug is the problem? It could be fried totally. ALways check to see if it works before u hand money over. hopefully you didnt get ripped off. How much did you pay?