I just spent half the day trying to do this. Lessons learned.
1. Don't use a headphone cable. They have Teflon, Kevlar, or whatever those strands are that refuse to get out of the way. And then you have to melt the enamel off the wires which never seems to burn off all the way. Use an extension cable or a thicker cable that came with PC speakers. They usually have 3 rubber coated wires LEFT, RIGHT and Shield (Bare).
2. Don't go back and forth between the picture of the radio and the wiring diagram. One is upside down and it will confuse the snot out of you. Especially since one is labeled 1234 and the other is ABCD.
3. Not sure why but when I pluged it in upside down my radio allowed media mode but had no audio. Not sure why that worked the way it did.
4. I wired RIGHT to 3(2C) and LEFT to 5(2E) and split the audio shield between 4(2D) and 6(2F) and left 2G empty. This resulted in the LEFT and RIGHT being out of phase with each other which doesn't make any audio or electrical sense at all. I moved the pin from 6(2F) to 7(2G) and everything sounded fine.
5. The shortest most difficult connector to plug in is the radio cable. the other one is for AC I think.
6. I was delightfully surprised that the radio remembers different volume levels for each source.
7. To pull the pins out of the CD audio cables a safety pin works best. It's sharp strong and wont slice your finger open.
8. I soldered the headphone cable directly to the pin. I hate soldering two wires toghether it never holds well. I used an old IDE drive to hold the pins still while I soldered.
9. IDE cables don't fit. The pins are distanced just slightly too small to just lop off the first 16 pins of a floppy cable. (that was the first hour of my frustration)
No one has posted pictures of their completed headphone adapters so here is mine.
https://www.dropbox.com/s/msncn5gzpkcap3x/IMG_6390.JPG
I flipped the diagram, duplicated it, and added numbers to help clarify which pins are which. This orientation is with the radio and "FM75Ω" right side up.
https://www.dropbox.com/s/u0pbjxyccqph453/auxcon2.gif