I posted this in the 90 forum, but I just saw there was an audio one so I figured I'd post here too. I couldn't find my answer in any old posts.

I'm wiring in a differnt head unit for my 89 90Q, with the factory amplified rear speakers. I also have the thing on the rear deck for headphones, not sure if that makes a diff.

I am trying to still use the rear speakers, at least for the time being, so I was planning on trying to power the amps and wire them to the preouts on my deck. I'm kinda lost at his point on how to do that.

I have it hooked up so that the fronts work fine right now, I used the scosche VW01B harness to connect the 2 lower plugs, but there is still the third plug mostly unconnected.
I did connect the wires, which seemed to be diagramed as the L and R wires from the top of the stock deck, to RCA ends and plugged those into my deck. I got no sound from the rears. I also tried connecting what seemed to be the grounds (two wires were together in the factory plug) to the main ground from the decks power, but that did't work either.

Anyone know what wires I need to hook up from here? Also what colors they should be?

Thanks in advance for any help

Conor

The Audi amp is puny and the lo level wiring to it is shockingly bad, so even if you get the right adapter and get it working it is likely you'll get engine whine from it.
You're probably missing the remote on connection, which is why you're getting nothing from them at the moment. You need to connect your pre-outs to the left & right pre-outs connector detailed on the old HU (sounds like you've already done this), then find the remote on connection (detailed as a switched live on the old HU on the same connector as the pre-outs), and connect this to the remote on/power antenna feed from the new HU.
But best bet is to disconnect the rear amp and run new speaker cable directly to the rear speakers.