|Left earphone channel
|Plugged-in detection (if shorted with Tip Side-A)
|Right earphone channel
I needed to change the female miniplug connector on my iPod Touch 2G, and instead of using an official propietary replacement I soldered some cables and took them out of the chassis, and added a female miniplug, and a switch to turn on and off the internal speaker.
NOTE: I'm almost completly sure about the Left/Detect sides, but this might be the other way around.
I've discovered that in my model (iTouch 2G), music always comes out of the channels, even if the plugged-in detector is open. In this case both the internal speaker and external earphones do play music. So, you might try to test this before deciding which side is the Detect and which the Left channel output.