When fitting a selection of handsfree kits to the Saab 9-5 2006 / 2010 the 10/400 lead is required. This is because some SAAB models have a factory amplifier on board so when adding an aux or phone kit the audio is too loud, the 10-400 allows you to reduce the volume levels going into the amp resulting in the ideal audio volume when fitting add on items, works very well with Parrot's Mki range.