I bought the Metra 70-1787 harness for my B5 A4 to install a new Sony head unit, and I can't figure out what to do with one wire (and I hope this is the reason the powered rear speakers are getting no sound.) The wire in question is grey-blue in colour, and you can see it jutting out of the red clip in the picture below:



I have no idea where that sucker goes! In addition to that, there is a similarly coloured wire loose in the package, with a flat-end connector, waiting to be inserted into another clip -- perhaps the black one?! The sales guy mentioned that this is the "trigger wire" or something to that effect. I see now that I should've asked follow-up questions! Any help or leads would be appreciated. Thanks, Audi guys.

 

The wire you are reffering to is the amp remote turn on wire. This connects to the amp that is stock in your car if you have the Bose system.The amp is located in the trunk.

The wire needs to be connected tothe remote wire of your deck if it has one or a keyed power source.