Thread: '05 GTP Stereo

My 2005 GTP came with an AUX cord connected through the back of the stereo, where I cannot easily access it. The cord does not pull loose so it must be connected to something. However, when I press the AUX button on the stereo, nothing. Is there some easy way to diagnose what the problem may be?

To be clear, I have the stereo that looks like this