Audio Systems: 2002 chevy avalanche factory radio replacement, chevy avalanche, c5 corvette

Question
I have a 2002 chevy avalanche and i am installing a new head unit. I have done many installations before however, after using the correct aftermarket wiring harness and pluggin it into the avalanche harness, I get power and all normal functions fine, but no sound through the factory speakers. This is not a Bose System either. I connected a test speaker to the speaker out put from the head unit and sound is going from the headunit fine. Just not making it to the factory speakers. Could this be becuase of a factory amp? If so, how would i bypass it and where would i find it. Do i need a separate interface to connect a head unit? ( like a C5 corvette Bose System Does ) Please help. thank you

Answer
Hi Joe!
You're close enough, but i got bad news for you, some GM cars use an amp that will turn on with Data signal on the CAN bus that means that if the radio does not send the data to the bus the amp will not wake up the easiest way around is to re-wire the speakers to the new radio. The amp is under the center console. A detail to take in account is that the door chime and the onstar will not work with an aftermarket radio, also if you install another factory radio in your car, it needs to be coded by your GM dealer.