Where is the factory amp in a 2004 Chevy Avalanche?

The factory amplifier in a 2004 Chevy Avalanche is typically located under the rear passenger seat. However, it's not always there; some models may have it in a different location, or not have a separate amplifier at all depending on the sound system options selected when the vehicle was new. You should check under the rear passenger seat first, but if it's not there, you might need to consult your owner's manual or a wiring diagram for your specific Avalanche trim level.