Sorry for the title but lets see if I can make it clearer here.
I have just done this on my 2001/2002 4.0L V8
Jaguar Premium Stereo with AMP under shelf and 6 disc changer in the boot, changer has a 12 pin plug, not the Ai-Net plug.

I finally found a simple and working solution to putting an AUX-IN to my S-Type. All I wanted to do was have Planet Rock blasting out my speakers as and when I wanted it, but with out the expense and hassle of replacing the stock head unit and probably custom making a new surround because nobody does one that looks nice enough, plus I think a more modern double din unit would look out of place.

So really all I wanted was an AUX-IN socket.
AND I FINALLY FOUND IT.

Must say a big THANK YOU to EDDIEV on Taurus Car Club of America forum where I found this info.
The other great thing about having the AUX-IN socket this way is the lack of any special skills or tools required, and the bonus is, if like me you are playing your tunes or listening to DAB through your mobile phone, then you get an in-coming call, it cuts the radio and you have hands-free conversation.
But it is not true hands free calling, so remember that please.
The only down-side if there is one is that you cannot use the cd changer for music anymore, but no great loss in my world.

To the details then.
In my car I have the Jaguar Premium Sound with the Clarion 6 disc changer in the boot. This changer has the 12 pin plug going into the side of it. THIS IS NOT THE Ai-NET set-up that is in the later models.
All the work is done behind the head unit in the dash to just the changer plug.

Here's the diagrams:



When you've done this, just burn an 80 minute cd with nothing but silence on it, put it into the changer and away you go.
If for any reason you get some ignition interferance, you can quite easily double up the earth lead and send it to the chassis of the car, also behind the head unit.

Hope this helps in the quest for the elusive AUX-IN problems.