Car Stereos: hard wiring chevy trailblazer, digital control signals, seatbelt reminder

Question
Hi i was trying to hard wire a 2004 Chevy trailblazer and when i went to hook up the after market stereo i could get it to power on for a second and then it would power of and i was wondering why that was. And also wondering if it could be done this way without any wiring adapters and if so what is the wiring diagram for that particular model of car...

Thank you

Michael

Answer
Hi Michael,

I always recommend using the proper wire harness for any head unit installation.  An adapter harness helps prevent all sorts of problems, and makes radio replacement and troubleshooting much easier later on.

Your problem is caused by the design of the factory audio system. An after-market head unit requires a constant power connection and a key-switched power connection.  In the Trailblazer, there's a constant power wire, but no key-switched (accessory) power wire.  The factory radio doesn't use an accessory power connection; instead, it's switched on and off with digital control signals through the vehicle's data bus system.  Your deck is switching on briefly when it's first connected, but you can't turn it on afterwards because it can't tell when the key is on.

Also, you'll find that the stock radio generates all the vehicle's warning chimes.  If you remove the radio, you'll lose the warning chimes (door chime, seatbelt reminder, headlight chimes) unless you use a special adapter, which can be fairly expensive.

If you buy the data bus adapter, it will include an output for the accessory power connection.  It will also generate all the vehicle's warning chimes in place of the factory radio.  The exact adapter module you need depends on whether the Trailblazer is equipped with a factory Bose audio system, and whether it's equipped with Onstar.

If you don't have a Bose system, you can replace the radio using a standard wire harness.  You'll lose all the audible warning chimes, and you'll need to connect the new head unit's accessory power wire to a key-switched power source at the fuse box or ignition harness.  Keep in mind that the warning chimes are an important safety feature--warning you when your door isn't closed all the way, for example.

Hope this helps!

Brian