I have found a lead on another forum that says that if you install it , you open up
the 'AUX' channel on the head unit , and can attach an iPod WITHOUT losing CD-changer or cassette modes .

However , the head unit they have displayed with 'AUX' , below ;

is not the same unit I have fitted to mine ;

Now , I have found this clip on YouTube ; http://www.youtube.com/watch?v=5dR_LZFzS1w describing
fitment of what I believe is a similar lead , and it intimates that by installing in a 'spare' plug behind the
head unit , that one keeps use of all operations radio / cassette / cd charger / aux .
Can anyone confirm if this is the case pls ??