okay so I have an '06 F-150 with the stock stereo, but the stereo has AUX button. However I can't find the aux input on the back of it. It's the stock stereo with 6 CD disk changer, but I can't find the aux input in the back of the stereo, could anyone plesae help me. Thank you.

 

The aux button uses the 16 pin port on the back of the radio. Have to have a harness of some kind plugged into it for it to work.