1998 pontiac bonneville

What are you trying to do? If you are just trying to add subs to a factory radio, buy a line output converter and connect it at your rear speakers. And future knowledge just assume no factory radios have RCA outputs on the back of them. I have only seen 3 in my life. One was a factory bought kenwood in a Tiburon, One in a Lambo Truck, and I forgot the other one I think it was an alpine in a BMW. So 99.9% your answer to that is no.

Ok thanks for your answer. What I have is a Premier 800W Amp and a Premier 12" sub Ported (In a box by SubZone) I also have a pair of Kennwood 6x9 but not sure I will use those as the stock Bose system already sounds good.  But Id like to form a Fiberglass box for the Amp/Sub to make it look kinda factory cause not much space.  I am trying to hook those up to the factory radio. I have all the wiring and a jack for the RCA outputs but the installers that did my last car just spliced them to the other car they were in so I have no idea where to splice them in the new car. I will take pics of what I have if you like to give me some ideas on installation for the new car. I was in a car accident and had to take out the system for my new vehicle. Thanks again, in advance.

You will have to splice you LOC into a rear speaker, NOT the factory sub, because that is self amplified. Your standard GM colors will be on the speakers and the darker of the two are positive. As for your 6x9's just leave them until the next vehicle. The factory bose speakers are fine, and they actually have a different ohm load than your kenwoods. Also the factory enclosure is a bit awkward if I remember. So in general, just do the sub/amp.