Monster MotorsportChris Nott
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  1. #1
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    Help.. not getting power through the 'constant' feed for the stereo

    Hiya,

    trying to install a new head unit in my A4 (2005 B7 - Symphony II), all is well apart from the voltage coming from the 'constant' feed, it seems to be between 4-6volts instead of 12V - and the unit won't work without 12v from both the ignition and constant...

    My Symphony was working fine, memory ok etc..

    Thought it may be the fuse... but can't see from the manual which one it would be and don't want to take them all out...

    Any help really appreciated..

    cheers

    Paul

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  3. #2
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    Symphony II only has a constant feed where are you getting the switched feed from?

    It uses canbus to power up.

  4. #3
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    user66252_pic96015_1082491683.jpg
    Hiya,

    There is a switched feed on the black connector - i.e. the + in the top right - the constant is the K....

    does that make sense?

    I have tested the + it is only powered when the ignition is on

    cheers

  5. #4
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    The K is the dignostic wire for the symphony radio, the + is the main live feed it should not be a switched live.

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    I'll double check that sorry... where is the switched feed then?

  7. #6
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    Doh.. you're right the + is constant... so do you know where there is a switched one? the stereo won't work without both..

  8. #7
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    Go to the fuse box, and fine a switched live.

  9. #8
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    Or wire both yellow and red feeds on the new HU to the constant live and switch the HU on/off manually
    "How to tear apart the ties that bind, perhaps fcuk off might be too kind"
    Alex Turner

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    Thanks for all the help,

    How easy is it to attach a wire to the fuse box (never done that before - but willing to give it a go) and does the fuse rating matter?

    according to the manual, the radio fuse is 20amp - so I suppose one that was the same would be ok?

    cheers

  11. #10
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    Hiya, tried the wiring the two together... and it won't switch off :-(

  12. #11
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    You may also end up with a power drain on the battery (depending on the radio) Just find one of the wires which is switched and just tap into it. You don't need 20amp for the switched live, just try and find one that is not connect to an important device I.E Engine ECU, ABS etc.

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    Ok.. suppose the Cigarette lighter would be an option then... I know which fuse that is.. looks like I have to take the fuse box out to get to the wires... is that correct?

    Looking at the diagram there is a switched wire in the 'line out' of the triple plug (bottom left) - could I use that?

    Geez never thought this would be soooo hard :-)

  14. #13
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    That's a line out of a radio that you have removed, so that's not going to work. If the cig lighter is switched live then go for that.

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    Bit dark now... will have a go in the morning...

    Thanks for your help..

  16. #15
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    That looks like mine (2005 A3) - if it is, as mentioned above, there is no switched ign feed like on old traditional stereos. The set takes all power from the constant feed and it "senses" the ign on and off via Canbus (as S8Craig said). You need to connect to the 20 pin mini-iso - there should be one (again if the 2005 A4 is similar) - you need to plug that into the back of your head unit so it gets the canbus signals.

  17. #16
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    The cig lighter is permanent live IIRC
    What HU are you fitting?
    No HU will not switch off if you have a live on both 12v feeds - that would mean you would have to have the stereo on all the time you're in the car whether you want it on or not. It won't drain the battery, the switched live does not drain any current if the HU is turned off
    "How to tear apart the ties that bind, perhaps fcuk off might be too kind"
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  18. #17
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    You'll need a repair wire from audi to fit into a spare fuse point, I cant recall which fuse points are ignition switched on a B7, but on the 8P for example, fuses 1-11 are, but a simple meter on spare points will advise easily.

    OEM RETROFITS - CRUISE CONTROL - SAT NAV - BLUETOOTH - AMI - HEADLIGHT SYSTEMS

    PARKING SYSTEMS - DIAGNOSTICS - FAULT FINDING - BODYWORK - PAINTWORK

  19. #18
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    Hi all,

    Thanks for all the help and advice, managed to find a point in the fuse box that was switched and tacked on a fuesed feed from there..

    All working now..

    cheers

    Paul

  20. #19
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    You tagged onto an existing fuse point that is being used by other systems?

    OEM RETROFITS - CRUISE CONTROL - SAT NAV - BLUETOOTH - AMI - HEADLIGHT SYSTEMS

    PARKING SYSTEMS - DIAGNOSTICS - FAULT FINDING - BODYWORK - PAINTWORK

 

 

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