Car Stereos: Installing aftermarket stereo, 2004 chevy trailblazer, chevy trailblazer

Question
Hi Brian,
    I have a 2004 Chevy Trailblazer whose CD no longer (or maybe never did) recognizes CD-R's. I'd like to replace it with an aftermarket unit. I am concerned because Crutchfield says it needs an expensive adapter thing so that the door chimes etc. will continue to work. I also note that it has the flashing light for the alarm system on its face, so I wonder if that would be non-functional as well. Can you tell me what I need to do to replace this thing. In the old days, you hooked up the power and the speakers and that was it. Is it more complicated now? Thanks a lot for your help!

Answer
Hi Fred,

In your Trailblazer, the factory radio is integrated with the vehicle's data bus system. GM uses the stock radio to generate all the system warning chimes: lights left on, seat belt reminder, door chime, and so on.  If you remove the factory radio, you'll lose the chime functions unless you use an adapter module.  The exact module you need depends on your factory options: if your Trailblazer is equipped with a factory Bose system, you'd need a different module than a non-Bose vehicle.  If you have Onstar and want to keep it working, you'll need to pick a module that retains the Onstar function as well.  

If you don't care about the chimes, you can use a standard wire harness to replace the radio.  Keep in mind that the warning chimes, particularly the door and seat belt chimes, provide an important safety function.  Also, if you use the inexpensive harness, you'll need to do some extra wiring.  This is because the factory radio harness does not include a key-switched power wire, but an after-market head unit needs this connection.  The chime adapter modules also produce a switched power source for the after-market deck; without it, you'd need to run a wire to a switched power source elsewhere in the vehicle.

If you have a Bose system, you can't use the inexpensive harness; you need the adapter module to properly integrate the Bose amplifier with the new head unit.

The "alarm" light on the factory radio is for the Theftlock system.  This is an anti-theft system that's just for the radio; it locks the radio if it's moved to a different vehicle.  It's not related to the Passlock II vehicle anti-theft system, or to the factory alarm system; and it's not something you'll need to worry about when you're installing a new head unit.  The only time the Theftlock system will cause a problem is if you try to use the stock Trailblazer radio in a different vehicle.

Hope this helps!

Brian