heineken

If you can find a wiring diagram of the wires to your headunit and amplifier (if you have one) I may be able to help you. I am assuming you are using the stock headunit. A 4 pole relay can be installed inline with the speaker wires along with a switch which will change between an AUX IN channel and the headunit. Volume and other sound functions can be used as normal on the headunit. This is how I have mine done: http://my.is/forums/showthread.php?t=277880