QuestionHi Brian,
I would like to upgrade my stock radio (6 CD Bose system) and speakers in my '08 Trailblazer but I am reluctant to due to Chevy/GM's "hard-to-install" procedures. I don't know what size speakers to get (Crutchfield told me 5.25 other websites said 6.5).
I was also told to get a harness to keep my door chimes and Onstar when I get the headunit which will be a Pioneer Premier Avic F-90BT. This is getting to be confusing especially installing the items myself to save some money. Can you please let me know your expert opinion on what parts I need (any kits, harnesses, diagrams, etc...)? Thank you in advance.
AnswerHi Alex,
Your vehicle should have 6.5" speakers in the front doors, and 5.25" speakers in the rear doors. (Technically the front door speakers are a 7" GM style, but most 6.5" speakers will fit without much trouble).
You'll need a special adapter to keep your door chime and Onstar working; but the exact adapter you need depends on the speakers.
Because you have the Bose package, there's a factory amplifier in the vehicle. If you elect to keep the stock speakers, then you'd need to keep the factory amplifier working with the new head unit. In this case, you'd use a Metra GMOS-04.
If you replace the factory speakers as you're planning, then you'll want to bypass the factory amplifier and connect the new speakers directly to the head unit. (Because the Bose amplifier uses internal crossovers and equalization, it's best not to use it unless you're keeping the Bose speakers). One way to do this is to run new speaker wiring from the head unit directly into each door. Another way is to run the speaker wiring to the factory amplifier location, disconnect the amp, and connect the wires from the head unit to the factory speaker wires at the amplifier. The Bose amplifier should be located under the side panel, above the rear wheel well on the passenger side of the cargo area (unless you have the extended version of the Trailblazer, in which case the amp might be on the driver's side). Any factory dash speakers or separate tweeters should be left disconnected.
If you bypass the factory amplifier in order to replace the speakers, then you'd need to use an adapter module designed for a non-amplified system. This would be Metra's GMOS-01.
In addition to the adapter harness, you'll need a mounting kit. You have a few options here: Metra's 99-2003 kit includes a double-DIN option, and it would probably be the easiest kit to find in a local store. You can also use an American International GM-K422 or a Scosche GM1590AB kit.
You'll also need an antenna adapter: Metra 40-GM10 or similar.
If you decide to use the factory speaker wiring, Metra's 72-4568 speaker adapters will make the speaker connections easier. If you run new wires into the doors, speaker adapters aren't required.
I hope this is helpful!
Brian
