I've been out to my car to take some photos.
Here is the setup in my car:
You can see the blue 12-pin connector in the quadlock and the red 20-pin connector with three smaller connectors in it - blue, green and yellow.
Here is a closer look at the 20-pin red end:
You can see here that there are three connectors joined together - a 6-pin yellow one, a 6-pin green one and an 8-pin blue one. This blue one is the one that is on the end of your CD-Changer cable. The bag the CD-Changer cable came in should have these additional connectors in it.
Here is the connector on its own:
You should be able to see the brown earth wire running across the top of my finger - this is attached to a bolt in the dash for earth.
Here is the 8-pin blue connector on its own - I presume this is the blue pin you are talking about.
Does this explain things for you, or do you need more information? Let me know if you do, and I'll do my best to help.