Car Stereos: Installation, stock stereo, rear speakers

Question
I have a 2004 Chevy trailblaiser with a stock stereo not the boise, my son wants to install 2-15" speakers and a amp w/a head unit...to take the stereo out do i take out the single screw in the storage area next to the 12 volt plug and then snap the plastic off that surrounds the stereo?..also the stereo now will some times play the back speakers and mostley not, would that be a bad connection at the stereo or the speaker?

Answer
Hi Melvin,

Sorry for the delay in answering this question.

You listed your location as the UK.  If this is correct, I'm not sure if the dash setup in your Trailblazer is comparable to the vehicles sold in North America.  In the American Trailblazer, the main dash bezel surrounds the radio and climate controls, as well as the instrument cluster.  There's a screw next to the 12-volt plug, yes; but you also need to remove a pair of screws above the instrument cluster before removing the entire dash panel.  

If both the rear speakers are coming in and out at the same times, then I'd suspect a problem in the radio, rather than at the speakers; but it's also possible that there's a problem with the rear seat audio controls (if equipped).  Vehicles with rear seat audio controls have the rear speaker wires routed through the rear control panel, at the back of the center console.

Hope this helps!

Brian