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Wiring in an aftermarket head unit, but found things I didn't expect. Help?

Discussion in 'A3/S3 Forum (8L Chassis)' started by grue, Mar 15, 2013.

  1. grue
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    grue New Member

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    [Mar 15, 2013]
    So I got my Concert Cassette unit out to install a new Pioneer unit, and found some… oddities, in the wiring… when I removed the adapter to use the Blaupunkt CD changer in the back with the factory HU, I was left with this:

    [​IMG]
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    Judging by the antenna mount left on the windscreen, I'm guessing there was a handsfree installed at some point, but I don't know what the spliced-in wires and fuse are for specifically. I went poking around and realized there's a factory amp or sub or something in the back, yet another surprise


    Here's my adapter:

    [​IMG]
    [​IMG]


    As it stands now, it looks like if I use things as they are, I will not get anything from my rear speakers, is that correct? What do I need to do to use the rear speakers (and sub?)

    Furthermore, what else do I need to add (if anything) to make sure the HU turns on and off with the ignition, and dims the illumination when I turn on the lights? I seem to recall reading a thing about that ages ago, but not sure if it'll be an issue with this adapter harness.

    Happy to take more photos as needed.

    Thanks, guys,
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  3. AndyMac
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    AndyMac Moderator Staff Member Moderator

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    [Mar 15, 2013]
    Yes looks like someone has added in an AUX in feed to the stock HU for iPOD etc as the blue mini ISO plug is not original, or they never had a CD changer lead fitted as standard so have added their own. All you need is the yellow plug which is the feed to the rear amp. Get a PC9-404 RCA adapter and plug your rear RCA's on the Pioneer into it and plug the yellow plug into the other end. then attach the blue flying lead on the 404 to the power antenna feed or "remote" feed on the pioneer.
    Luckily you have an ignition on feed on the black power ISO so connect that to the power ISO on the HU. You will need to swap over the yellow and red feeds as Audi wire them back to front. Then plug the brown front speaker harness into the speaker harness plug on the HU.
    All you then need is an antenna amp adapter PC5-52, and again the blue flying lead needs to connect to the power antenna feed on the HU
    Ignore the big red plug and the CD changer lead as the changer won't work with the new HU. Remove the piggybacks (wrap some tape around any bare wire) and all the additional fuses that have been added
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  4. grue
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    grue New Member

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    [Mar 15, 2013]
    Awesome, thanks so much.

    If we say for the sake of argument I were able to solder decently, is there any reason I couldn't solder an RCA to ISO myself if I didn't want to order another adapter? I'm guessing all I need to do is solder the outer barrel to negative and the pin to positive for each channel?

    I do have the antenna adapter already, but since I know how to work that in I left it out of the pics :)

    When you say swap the red and yellow, just pop 'em out on the adapter and put 'em in each others' place?
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  5. AndyMac
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    AndyMac Moderator Staff Member Moderator

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    [Mar 15, 2013]
    It's mini ISO - it needs to plug into the yellow mini ISO plug - not something you would have kicking about in your connector drawer
    They sell them in Halfords or Maplins
    No, you can swap the yellow and red over on the Pioneer harness - second to last pic
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  6. grue
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    grue New Member

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    [Mar 18, 2013]
    Ok, everything's all wired up and technically working, but the sub and rear speakers are very very quiet even when I fade all the way to the rear. Dead amp?
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  7. AndyMac
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    AndyMac Moderator Staff Member Moderator

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    [Mar 18, 2013]
    Yes they will be, you have 2 x 50w+ now going to the fronts, and still a puny 2 x 20w going to the rears from the Audi amp. Ideally you need to rewire the rears directly to the HU and bypass the Audi amp, then use the sub pre-out on the RCA adapter and whack the sub level up to max. The sub will still struggle to keep up with the cabin speakers as it only has 1 x 50w max output competing with 4 x 50w from the cabin - an active sub upgrade would be money very well spent, something discreet like this 8" Alpine
    Alpine SWE-815 Active
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  8. grue
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    grue New Member

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    [Mar 18, 2013]
    By very quiet, I mean if I fade all the way to the rear, I have to crank it up and can BARELY hear anything from the rears still, and it's very muffled and rubbish.

    I might look into wiring up the rears directly, though… wouldn't be a bad idea. Turns out I need to replace the driver side main speaker as well in the front, it's blown. Argh.

    Do you sell the 4" adapters/ship to Australia?
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  9. grue
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    grue New Member

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    [Mar 18, 2013]
    Oh, and it seems like the HU doesn't automagically dim when I turn on the lights. Should it?

    Pioneer DEH-X6550BT.
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  10. AndyMac
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    AndyMac Moderator Staff Member Moderator

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    [Mar 18, 2013]
    Have you connected the blue flying lead on the adapter to remote on or power antenna? Sounds like the rear amp isn't turning on
    Adapters are on eBay
    The illumination control is on the big red connector with only one or two wires on it. Not sure if it'll work with the pioneer
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  11. grue
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    grue New Member

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    [Mar 18, 2013]
    Yeah, the amp and antenna leads are both connected, at least in theory. Might have to do a bit of continuity testing… hopefully the amp isn't dead.

    The harness for the pioneer had an illumination wire left over, I'll try hooking it up to the one from the red block and see what it does :)
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