if you have a non-original headunit the audio mute is just a wire into the unit that mutes when it receives +12v (from phone kit or otherwise), if an original headunit has this facility it is usually an unconnected fly lead on the 'power' block of the two euroconnectors..
if both phone and headunit are non saab then its often easier! hope this makes sense
Mines a 1993 head unit and it doesnt have any spare flying cables at the back? There are a couple of pins that are not connected on the main power connector? Could it be one of those? Does anyone have a pinout for the Saab 9000 stereo? (before it changed to ISO)?
if the loom has a mute lead it will be flying not a spare pin because the only place you want to connect to is a phone kit, not anywhere else in the car. (a spare pin will go off someplace else for another connection)..
if its a din sized unit the saab handbook should tell you the pins on the two car loom connectors.. ive lost mine but my '91 has no mute facility on the original unit...
sorry i cant be of more help!