"Bulb failed" light illuminating when no bulbs are out, S124

Discussion in 'Electronics' started by OneCarefulOwner, Oct 6, 2010.

  1. OneCarefulOwner

    OneCarefulOwner Hardcore MB Enthusiast

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    The "bulb blown" light keeps coming on in my S124 when I turn on the sidelights, but all 6* bulbs I can see as belonging to that circuit are illuminating. If I use the P< or >P switch positions, the bulb warning light doesn't come on. Any ideas?

    * front n/s, front o/s, rear n/s, rear o/s, 2x number plate lights.
     
  2. FazMan

    FazMan Member

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    I had a similar problem, luckly mine was an easy fix, I just took out the bulbs and cleaned up the points of electrical contact.
    Worth gently tapping the lights to see if any flicker due to a poor contact.
    I found that the warning light would stay on even if the bulb worked after a while. Probably senses an increased resistance caused by poor contact. Also it's possible for the filament to be broken but movement causes it to make contact and then it stays for a while and the heat generated forms a poor joint.
    I'd be very surprised if it was anything serious.
     
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  3. OP
    OP
    OneCarefulOwner

    OneCarefulOwner Hardcore MB Enthusiast

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    That sounds great; I know that resistance from LED bulbs can be different and cause this, but simple corrosion hadn't occured to me - I'll grab a scouring pad and give them a clean :)
     
  4. GP801

    GP801 Hardcore MB Enthusiast

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    Usually its the tail light bulbs (sometimes brake lights but this triggers warning light when pressing brake). Dont have to be blown. Circuit measures change in resistance and can detect changes before bulb actually blows. Also best replaced in matching pairs.
     
  5. b11ocx

    b11ocx Member

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    My experience is that the bulbs are about to blow......
     
  6. Smiley

    Smiley Hardcore MB Enthusiast

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    check that the tail light bulbs are rated at 10 watt - if someone has put 5 watt bulbs in there it will illuminate the warning light.
     
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  7. 230K

    230K Hardcore MB Enthusiast

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    What he ^^^^^says

    230K
     
  8. bolide

    bolide Hardcore MB Enthusiast

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    Early cars were 5 Watt, late cars 10 Watt. At least they were on the estates...

    Nick Froome
     
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  9. OP
    OP
    OneCarefulOwner

    OneCarefulOwner Hardcore MB Enthusiast

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    Mine's one of the last, so I'll double-check the wattage; thanks all!
     
  10. Andi968

    Andi968 Member

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    A little tip is this weather is once contacts are clean smear a small amount of Vaseline on connecters ensuring not to get any on the glass itself.
     

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