Hey, Trying to install Pioneer FH-X730BS double din headunit/stereo/radio in my a4 b6. I have a 70-1787 harness which has a red socket, and seperate black socket, and Metra 40-VW54 antenna adapter. The harness is color coded, and I connected each wire to its corresponding wire from the a4 harness. The left over wires from the matching up, is the Green , Green/Black STripe, Violet, Violet/Black Stripe, and a blue/white stripe with "REMOTE CONTROL" sticker on the end.

The antenna adapter plugged in to the pioneer unit, then connected to the a4 radio antenna. The red socket had violet, green, white, gray RCA connectors. I plugged the green and violet to the rear output on the pioneer unit. The black sockets were attached, all was correct as far as I could tell. Turned car on, no power, nothing changed.