Wire diagram or explanaition

Hello I have a 2008 Pontiac Grand Prix base model
and I am trying to hook up a Kenwood deck
aftermarket to it. I am trying to find out what I am
trying to find a diagram for the radio wiring harness
that explains the different colours the only diagram
that I find for the O8 does not have several of the
wires that my harness has and although I am told
that the 2004 to 2008 Pontiac Grand Prix are all the
same, every diagram did I find is different.  I have
been to the GM Pontiac dealership as well as the
GM parts site, and they will not or can not seem to
provide one for me. I have also showered the web
looking and have only managed to obtain
frustration and aggravation. I do not care about
OnStar because it has been discontinued, in my
year, make, and model, I do not care about the
Chimes because they are annoying, I cannot afford
navigation, besides Google is free, and I am on a
disability and unable to afford interface modules or
any of that other fancy junk. PLEASE CAR GIRUS
OF THE WORLD HELP!!!!!!!!