Recently bought a used 03 Honda Accord and it CAME with a USB Adapter that was installed under the little cubby area below the radio. I tried to see if it worked by plugging it in my phone and switching to Aux with the CD/Aux button but it won't switch to Aux at all. I really want to use Aux!
Do you think the Adapter might have been unplugged under there?
Do I need a new one?
If there is nothing plugged to the Aux is that the reason when I press the CD/Aux button it won't switch?

 

I'd pull that center "pocket" and take a look at the plug on the radio and your "added" connection to make sure everything is installed correctly.