does anyone have a pic of the rear of a 2002 wrx head unit or tell me what connections ar on the rear for a multichanger?

cheers

on the back of the double unit (i presume it's standard) there will be a mulit pin socket that will take the changer lead.

It should plug straight in. The Headunit is a kenwood model if that's any help (or at least mine was - 2001 wrx new age)