Upgrading stereo - quick question, three connectors

watercool

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Hi, just popping a new Pioneer head unit into my 2003 A3 as an upgrade from the Concert.

What are the three ISO box connector things for that come from the dash? A harness was included with the new stereo but only accommodates TWO of the boxes...

Also, what is the little yellowy brown box connector for on the right of the pic?

(I've plugged two of the connectors in to see if it'd work but it wouldn't turn on.
 
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