To clarify, you have an aux cable plugged into the headphone / aux hole of your iPod and into the same sized aux hole in your glovebox, correct? And no music. Presumably your car plays from other sources quite happily? If so I'd suggest it's an issue with the car. If you want to try an alternative method I'm happy to send you one of my cables (see photo above) and if it works you can keep it for what I paid for it.
As there seems to be no truly integrated iPod / car option on our cars (unlike the new Ghibli which works just fine with an identical cable) I'm wondering how the h3ll I convert an abundance of iTunes files into a different format and get them and all the associated metadata onto a USB stick.