i found lots of good information on cruthfield and other aftermarket sites when i replaced the stereo in the wifes car. several places have downloadable instructions that include everything you need to know.
good luck
I didn't buy anything from them but they have the drawings that show how the trim comes out and which wires are for what for free on their site. If it wasn't theirs it was another similar lower end site that had all the schematics for free. :shrug:
free information is a good thing