PCB- It's the green plastic wafer thing that looks like it has metal 'tracks' on in. These connect all the components together inside the sterio.
I'm talking bout the stock cd/tape/radio player here:
Take it out
Take the heatsink off
Take off any panels. We're trying to get to the 'bits' behind the wiring plug.
The socket for the plug will be soldered onto the PC Board. Follow the 'tracks' to see where they go. Next to each track should be white letters symbolising which wire does what. ie FR= Front right speaker.
If this is too vague (it sounds vague when i read it out loud ) just request me to pull the old sterio out of mine, and i'll take some photos for ya!