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Ingition Live Feed

Discussion in 'A4/A4 cabriolet/S4 forum(B6 chassis)' started by Marc1, Sep 19, 2009.

  1. Marc1
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    Marc1 Member

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    Anyone know a good ingition on feed to take power from to power a cig lighter mounted behind the dash and what colour wires are they, I amuse red and black? Also I have 15a mp twin core cable, will that be ok to use? Cheers
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  2. Garfie
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    Garfie Member

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    For my parrot bluetooth kit I hooked in to an ignition live in the fusebox. Check each fuse with a multimeter for a live one with the ignition on, when you find a live one turn the ignition off, if it then goes dead its an ignition live.
    Remove the fuse and turn the ignition back on and check which pin of the fuse holder is dead (the other should be live) Then go to the back of the fuse box and find the wire that goes to that dead pin. Splice your cig lighter positive wire to that wire and you have your ignition live.
    You will need to make sure the wire you use is capable of taking the max current of whatever device(s) it is that you intend to plug into that cig lighter plug. As long as its less than 10amps the 15amp wire will be fine (with a factor of safety included)
    As your new ignition live runs through the fuse you found in the fusebox you will also have to remember to uprate that fuse . For example, if it was a 15amp fuse and your device(s) draw a maximum of 10amps you'll need to change the fuse to a 25amp one.

    Hope this helps (and wasn't teaching you to suck eggs)
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  3. Marc1
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    Marc1 Member

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    That guide wad great thank you, it's exactly what I need. I've now found a few feeds that are ignition only. Horn 20amp and fog lights 15amp. The device to power is a max 6.5amp. Can I add it to the horn as that won't always be in use and leave the existing 20amp fuse?
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  4. J7USS
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    J7USS Shuddup Foooool!!

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    I took mine (for my live feed on the Boost gauge) from behind the Light switch IIRC.
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  5. Marc1
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    Marc1 Member

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    Cheers Juss. Did you need to use the negative too? Most of the things I've looked at in the fusebox seem to only have one wire going in, so asume only positive. As you can tell electrics are not my thing.
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  6. AndyMac
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    AndyMac Moderator Staff Member Moderator

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    All feeds are positive, negative is the cars chassis
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  7. Garfie
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    Garfie Member

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    Yeah for the negative just earth it to the chassis somewhere. You'll probably find a few existing easy to get to ones behind the dash. Just look for a thread somewhere coming from a piece of metal that has one or more brown wires bolted to it. A quick check with the multimeter taking positive from your selected fuse wire and negative to your selected earth point is worthwhile if you're not 100% sure, as long as it reads 12v with the ignition on you should be good to go.

    With regards to the fuse, thinking about it again, if the cigarette lighter plug on the power lead for your device already has a fuse inside the end of it that protects the device itself (i,e somewhere around a 6.5amp fuse), you can take your feed from the positive side of the horn or foglights fuse. This will mean the fuse in the fusebox wont need uprating.
    If it doesn't have its own fuse in it the the best thing to do would be to still splice into the feed from the positive side of the horn/foglight fuse, but get a fuseholder with a 7 to 10amp fuse in and use that on the positive wire of your cigarette lighter socket. Place it as close as you can to the point where you splice into the feed from the fusebox.

    Doing it either of these ways ensures both your device and the horn/foglights are protected by their own fuse, without the need to change the fuse in the fusebox.
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  8. Marc1
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    Marc1 Member

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    Thanks again guys. I had no idea the negative should be used to earth. I have seen a load on earth points behind the dash with brown wires attached, so I'll do the same. If this is the case, could I also add the postive wire to an empty slot on the fuse box and add a 10amp fuse and the circuit work as I assume there is a main live to the fusebox which powers the 'grid'? Maybe wrong there. ALso need to buy a multimeter, I only have one of the little pen things which is way past it's best now. Cheers again.
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  9. Garfie
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    Garfie Member

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    From what I remember each fuse has its own positive feed via a wire, they dont work from a common live thats fed directly into the fusebox.

    Yes, you could splice a wire from your chosen ignition positive wire and take it to an empty slot in the fusebox to have a factory fit look. It may be more hassle but you may be lucky and find the fuse holder and wires are available from audi.
    What I did on the Golf was to buy a stand alone spade type fueholder from maplin and just fixed it in place beside the fusebox. It wasnt to factory fit standards but was still accessible when you open the flap on the end of the dash.

    Just remember though if your devices cigarette lighter plug has a fuse in it already then you wont need another fuse anyway. It wont do any harm but wont be worthwhile if its the fuse in the plug that actually blows first.
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