Akright 2008 GT Coupe w/monsoon. I have premier deck, components, amps, subs etc from my 2007 silverado. Now question is do I have to install that $140 onstar wire harness? I want to get my Premier stuff in there but that expensive harness has been holding me back. I have all the wiring/harness connecters from my truck. Lemme know. Thanks just not 100% with monsoon and onstar.