Do you need to keep factory radio in a 2004 Chevy trailblazer replace with an aftermarket head unit?

No, you do not need to keep the factory radio in a 2004 Chevy Trailblazer if you're replacing it with an aftermarket head unit. You can remove the factory radio entirely. However, you will likely need a wiring harness adapter to connect the aftermarket radio to the vehicle's existing wiring. This adapter simplifies the installation process and prevents the need for cutting or splicing wires.