What parts do I need to put my sub/amp/aftermarket deck in? 2003 Ford Explorer Sport Trac?

I just need to find out which wiring harness I need to connect my harness('s) from the stock side to the deck side harness.. I understand they make a harness but there are three coming off the stock side, and the connector harness I found only comes with one harness? and I bought a Scosche pn: FD3090 dash kit to plumb in the new deck but it is too wide to fit into the stock din, I need a solution to these two problems, any advise or part #s would be greatly appreciated.