audio amp install

I want to install an audio amplifier to my factory sound system on my 03 gm Sonoma. Can anyone help me determine which wires at the back of my factory am/fm cd deck (with RDS) are the speaker wires. I need to find which wires go to which speakers and also whether or not there is a terminal there which would turn the amplifier on and off.Or maybe someone could suggest which website to go to for this info.