So I connected the plug cable to

pin 18 = Changer input (-)
pin 19 = Changer input left (+)
pin 20 = Changer input right (+)

What do I do next to make it work ?
There are more pins.

pin 13 = Changer signal
pin 14 = N/C
pin 15 = Negative supply
pin 16 = Permanent 12 V +
pin 17 = Switched 12 V + (rem)

Thankful for good advices
"The Bumperman" (he, with "Cowcatchers" on his smart)

Over here the radio 5 is standard only on the smart ForFour so won't work.
The fortwo stereo never had a name.

Considering I sell these leads to fund my website, i'm hardly about to tell everyone how to make them am I?

I respect Your arguments, keep up Your good work with this
very professional and informative site !
Best reguards, Lasse
"The Bumperman" (he, with "Cowcatchers" on his smart)

P.S. (later same day)
Someone others knowledge made the trick and spared me some 160 SEK.
After looping pin ?? & ?? and one push on ?? button
AUX appeared in the radiodisplay. Now I can connect my
Sony Ericsson K750i (with 1G memorycard), and listen to
all CD ripped mp3-music without any breaks on bumpy roads.

Lasse

looping pin 13 and 15 and push on CD button for AUX. Signal for Ipod pin 18 GND, 19 Signal Left, 20 Signal Right

rectify a 33 kohm resistor between pins 15 and 19