The aux. button is used to access the dvd function of the radio, if the truck doesn't have FES(family entertainment system) then the aux function isn't used. I use this button on my explorer to run mine. on some models they did have a port in the back to run a cd changer, but you had to pull the radio. I double checked and read the owners manual online for the 05 f150 and it reads the aux is used to access the dvd function if the vehicle has it.