First thing I'd do as a newb is find an ebay hardcopy or get get an online subscription to the FSM. Only AFTER that would I check the (very detailed) wiring schematics to ascertain whether the general rule applies that close to 80% of fellas doing their aftermarket systems have managed to pheuch up at least some of the wiring. Finally, I'd be trying to recall real hard whether I had noticed the rears weren't working WITH the existing, or, they just didn't make sound AFTER you replaced it. And of course while you didn't mention it, it's kinda important to know whether the replacement an oem radio or just something else aftermarket? And was it brand new or used? Lotsa variables to track down and weed out..... any troubleshooting recommendations? A Noob here..