connecting 3.5mm jack to tuner

[DaDangerMan]

hi people well as im a mingebag and enjoy trying stuff myself i am trying to connect a 3.5mm jack to my tuner list headunit, i got a diagram on the cd changer (8 pin iso) slot and got this info

Pin 13 - CDC data in (bus)
Pin 14 - CDC data out
Pin 15 - CDC +12v permanent
Pin 16 - CDC +12v switched - maximum 300mA (+A)
Pin 17 - CDC data ground (+U)
Pin 18 - CDC audio frequency ground
Pin 19 - CDC audio frequency left
Pin 20 - CDC audio frequency right

so i got a lead i had around house which was a phonos to 3.5mm jack
snipped it in half and not have a 3.5mm jack with 2 wires i connected 1 to pin 19 and the other to pin 20 so thats my phonos connected, so tried this and cant get cd changer on its not on source i get cd fm am thats it.
so i looked on ebay at some and they look like mine , and found one which had a wire looped , and seeeing im not needing power to go to my mp3 i dont need it so i fort it must be data in to data out which i done and still cant find cd changer,
is there something im missing, simple way to get to cd changer on this unit, i had an aftermarket headunit in so this one is new to me, ?

any help much appreciated