Ok, so I am looking a buying a car stereo, I am buying the head unit, and a seperate HD Radio add-on tuner.. I want to know, once I hook up the wiring harness, will my OnStar system still be fully functional? I am driving a 2006 Saturn Ion2 4dr Sedan, head unit I am looking at purchasing is the Sony MEX-BT3800U, and the HD Radio tuner is the XT-100HD. If the OnStar system will not be fully functional, is there a part I can buy to make it work?