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Wiring in a proper accessory feed (ignition on) for aftermarket HU install

Discussion in 'A4/A4 cabriolet/S4 forum(B6 chassis)' started by AndyMac, Nov 10, 2010.

  1. AndyMac
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    AndyMac Moderator Staff Member Moderator

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    [Nov 10, 2010]
    2000+ Audi's don't have an ignition on feed to the HU. They use the CANBUS to tell the HU when the ignition is on, and when the keys are pulled out.
    You need to either pair the permanent live with the ignition on feed to the new HU and turn it on/off manually, or create an ignition on feed for the new HU.
    Unfortunately there is no easy feed to tap into. They are all either perm live or only live when ignition is fully on i.e. they go off when you turn the ignition off and don't stay live until you pull the keys out, which is what you really need.
    If you don't mind the HU turning off when you turn the engine off then you can tap a feed at the fusebox, there are plenty of options there.
    If you want a proper ignition on feed i.e. the HU stays on until you pull the keys out, then you need to wire in a relay. The trigger to use for the relay is under the steering column. Remove the trim under the steering wheel and you will see the main loom from the ignition switch running under the left side of the steering column. You'll see some black trunking protecting the loom. Release this trunking so you can get to the wires. You'll see a very thin red wire in amongst all the other thicker wires. This is the one you want.
    With the ignition off and the keys out, chop this wire and reconnect it with a small terminal block along with another wire that you can then run to the relay. Unfortunately the wire is so thin that you can't get a reliable feed using a piggyback connector.
    This is a very low current feed so you can't power the HU directly from it. Just wire in a 12v relay using piggyback connections from the perm live & earth at the HU and use this new wire to switch the relay on/off, then use the other side of the relay to power the HU. Sounds more complicated than it actually is, took me 30-45 minutes to do mine, but well worthwhile otherwise you need to have the keys turned to ignition on to get the HU to work when parked up.
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  3. Encabler
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    Encabler New Member

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    [Nov 29, 2010]
    If I'm not adding an aftermarket HU, can I pick up the switched power lead which runs to the factory amp in the boot to turn on a couple of amplifiers? Or, is this still not a typical ignition lead? Thanks for the help.
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  4. scott b
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    scott b Active Member VCDS Map User

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    [Nov 29, 2010]
    just get a multi metre out and test the feeds
    #3
  5. RobMorris
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    RobMorris Member

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    [Mar 4, 2013]
    Hi Andy

    Do you have pics and or a diagram to for the above?

    Cheers
    #4
  6. AndyMac
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    AndyMac Moderator Staff Member Moderator

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    [Apr 7, 2013]
    [​IMG]
    [​IMG]
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  7. JTL
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    JTL New Member

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    [Aug 12, 2013]
    Hi Andy
    Can you explain a bit more about wiring up the relay. There are 3 connections you suggest :-
    1)Trigger from steering stalk,2) Perm 12v to HU, 3) Earth to HU but shouldn't there be a 4th providing a circuit exit from the Trigger wire ? That can't be connected to the Earth I assume ? so what should I be connecting the 4th terminal to ? Apologies if I've got the wrong end of the stick or if this a stupid question ..
    Thanks

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  8. quattrojames
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    quattrojames Moderator Staff Member Moderator

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    [Aug 12, 2013]
    #7
  9. Mollygoogle
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    Mollygoogle Member

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    [Aug 12, 2013]
    He lists all four connection, permanent live, earth, switched live taken from the ignition live feed he describes and output to the headunit, etc
    #8
  10. AllyMc
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    AllyMc New Member

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    [Aug 12, 2013]
    Just fitted a switched accessory feed via a 4 pin relay for my double din Pioneer...

    Wire the relay as follows:

    #30 Permanent 12v live in from Car.
    #85 Ground
    #86 Switched source from under steering column
    #87 Switched live in to head unit

    Works a treat, and will stay live until you remove the keys.
    #9
  11. JTL
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    JTL New Member

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    [Aug 13, 2013]
    #10
  12. JTL
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    JTL New Member

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    [Aug 13, 2013]
    Hi Ally thanks very much for this information its exactly what I needed. Great

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  13. vwgtiking
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    vwgtiking Member

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    [Aug 21, 2013]
    Firstly , I like to say I am sad to hear that andymac has passed away.

    Which relay has everyone used? Do halfords sell it? And how can I get access to the wires. I've tried removing lower cowling before with no avail.
    #12

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