Compare the wiring with the actual wiring of your car to see if this codes apply.
http://www.installdr.com/Harnesses/GM-Wiring.pdf
but to istall an amplifier what you need to know is if the stock unit has pre amp outputs (RCAoutputs) to connect them to the amplifiers inputs audio signal. Connect the remote wire of the unit if supported, if not you will need a new line with an in-line swith or a relay if the only available wire is the antenna wire.
If the stock unit have no pre amp outputs, you need a line output converter to convert the high level speaker signal into a low volatge pre amp audio signal.
