Cd changer to iPhone

[Passat54lancs]

I have a 54 passat with Gamma radio tape deck with separate CD changer connected (all factory fitted) and works well.

I bought an iPhone lead to plug into the back of the CD player unit (the CD player had a blue connection socket for a CD changer which I don't have). Connected cable OK but the car doesn't let me select CD changer, the right LeD changes to changer then swaps straight back to CD mode.


Welcome ideas

Cheers