This is the drawing I made. I think this might be what you meant. I have updated this drawing to add the Aux input, and the Onstar connection needs a drain wire added to pin 5. I haven't uploaded my updated drawing because I still want to test it. My wire harness is about 80% done, but I have been distracted with other projects. I will complete it eventually and I will post all of findings so that others can make one.