Head unit modification on a 1999-2005 Saab 9-5 to add a line input for
  external media player connectivity.
  
  Parts of this guide are outdated, please search Saab forums for more recent
  solutions for adding a line input to a 9-5. You can still use this as a general
  guide on taking the stereo apart.
  
  A digital music player is an attractive and convenient source of music in
  the car, but the
  stock head unit does not have a line input. Many people end up using an FM
  modulator or a cassette adapter, which inevitably sacrifices the sound
  quality. Not everyone agrees to this compromise, especally if you have
  a premium Harman Kardon stereo in your car, or a custom upgraded system.
  
  There are several alternative solutions for direct MP3 player connectivity.
  This guide shows how to do it
  yourself by using the tape deck inputs of the internal amplifier. It is
  a relatively easy and inexpensive way to add a direct line input to your
  stock head unit without sacrificing any existing functionality.
  
  Thanks to Daniel
  Giertz and all the Saab forum members who did the research and
  contributed to the installation guide.