you need teh harness from amp and sub to speakers and radio. if you look at my diagram you can see what the connectors are all for. it is not one in and one out. also you need the connections to XM and onstar. he basically needs to give you the harness with the two radio connectors, amp connector and sub connector intact, and as much of the speaker and xm/onstar wiring as possible. then you need to blend them together in the car. you will have your old harness and new harness in there at the same time. you cant pull one out and put the other one in because there are wires that go other places.