Has anyone tried to add the two rear seat speakers yet? I can't seem to get a service person to give me a straight answer. My parts guy told me he could not get the wiring harness ordered. He said there was a picture of it but he could not order it. He says the wiring may already be there but I couldn't find it and the service guy told me that GM has stopped wiring for speakers not originally in the car. He said I would probably have to splice it into the wiring for the speakers in the rear doors. If someone has some experience with this I would really appreciate any help I could get.