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  1. #1
    VXRed blooded
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    Default anyone know which wire is 12v when headlights are on?

    I've recently got a new boost gauge to replace my old one and it has a feature where it lights up white and then when you put your lights on it changes to red, so in order for it to do that one of the places it needs to be wired into is "headlight switch 12v(+)" so presumably that's one of the wires that goes into the back of the headlight switch that gets power when you turn the lights on and i was hoping someone would know which wire that is? as i'm not really sure how to test it to find out which one it is myself

  2. #2
    VXR Adam"san" w20adm's Avatar
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    Do you know how to remove your headlight switch? It's dead easy and at least you'd have access to the loom where such wire lives.
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  3. #3
    VXR enough andrewt1971's Avatar
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    The headlight switch just signals one of the computer modules to switch the lights on the Astra, there is no +12v. if you want the gauge to light up with the headlights you will probably have to pick it up from the UEC.

  4. #4
    VXRed blooded
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    Quote Originally Posted by w20adm View Post
    Do you know how to remove your headlight switch? It's dead easy and at least you'd have access to the loom where such wire lives.
    yep i know how to pop the switch off, but if i remove the wires from the back of it so that i could put a multimeter on the terminals then i can't turn the switch to turn anything on and if i leave the wires plugged into the switch then i can't get a multimeter on the terminals to tell which one gets power when the lights are on, or at least that's what i'm assuming will be the case based off my memory of the last time i took it out, so thought it'd be easier if someone just knew "oh the orange wire gets power when you turn the lights on"
    Last edited by 4ftofflame; 10th February 2019 at 06:07 PM.

  5. #5
    VXRed blooded
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    Quote Originally Posted by andrewt1971 View Post
    The headlight switch just signals one of the computer modules to switch the lights on the Astra, there is no +12v. if you want the gauge to light up with the headlights you will probably have to pick it up from the UEC.
    first off, what's a "UEC"? second, the light switch itself lights up when you turn your lights or sidelights on along with all the other internal switches illuminating, so surely there must be one wire going into it that gets power when you turn the switch from off to the first or second position?
    Last edited by 4ftofflame; 10th February 2019 at 06:09 PM.

  6. #6
    VXR Adam"san" w20adm's Avatar
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    Underhood electrical center mate.

    Basically the fusebox in the engine bay
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  7. #7
    VXRed blooded
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    ah ok lol. i know what that is, never heard it called a UEC before. I still don't get how there isn't a switched power going to the switch. The switch itself lights up when you turn your sidelights or headlights on but isn't illuminated when in the off position so surely there must be something to tap into? or at least that's what it feels like should be the case but as i've proved i know nothing about electrics lol

  8. #8
    VXR Adam"san" w20adm's Avatar
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    The activation of the lit up dial is probably computer sent too mate
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  9. #9
    VXRed blooded
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    Quote Originally Posted by w20adm View Post
    The activation of the lit up dial is probably computer sent too mate
    bloody modern cars with their computers lol. I swear i spend half my time wishing parts on it were newer/better like the triple line display or the nasty amber colour of the internal lights etc.. and the other half wishing it was more old fashioned and easy/simple to do things on

  10. #10
    VXRed blooded
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    Literally all i need is a wire that doesn't get power when the headlights are off but then has 12v+ when you turn your lights on, i honestly didn't think it'd be so tricky
    Last edited by 4ftofflame; 10th February 2019 at 07:30 PM.

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