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Simple Circuit Help- Automotive Lighting Circuit

Discussion in 'Electronic Basics' started by Matt, Mar 16, 2007.

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  1. Matt

    Matt Guest

    Hi All, I'm hoping someone can help me, i have what is probably a simple
    problem-

    My car (Mitsubishi) has a dual filament stop/tail light for each of the rear
    lights (12v 5/21w), and a 3rd LED highlevel brake light.

    Incase your not familar with this setup due to this being an international
    newsgroup and i'm in the UK, when you turn your headlights on, the 'tail'
    light filament of the bulb illuminates (5w) and illuminates the red section
    of the rear cluster. When you press the brake pedal, the 'stop' light
    filament of the bulb illuminates (21w) and the red section of the rear
    cluster illminates brighter, also the red LED brake light illminates.

    I wish to replace the stop/tail light bulbs with LED items, these i have
    bought and fitted, however they give the following issue-

    They work fine in the cluster for stop/tail operations, but when in the tail
    light only (Lights on, but the brake pedal not depressed) a few LEDs in the
    high level brake light illminate dimly, if i replace the LED bulbs with the
    filament ones the LED remains extinguished in tail light only.

    Does anyone know why this is happening? I assume its something to do with
    the LED bulbs having lower resistance than the filament counterparts so some
    voltage is 'leaking' through to them? Can i put a resistor in the line of
    the power to the high level brake light to solve this? If so what value of
    resistor would you suggest?

    Thanks for any and all help

    Matt
     
  2. Matt

    Matt Guest

  3. Matt

    Matt Guest

  4. Tom Biasi

    Tom Biasi Guest

    If you purchased LED replacements for your cars tail/break lights they
    should work just by installing them. No resistors or magic wands should be
    necessary.
    When you say some LEDs are dim, isn't that the way they are supposed to be
    in the non-breaking condition?

    Tom
     
  5. Rich Grise

    Rich Grise Guest

    Where are you picking up the +12 for the third brake light? You might need
    an isolation diode - can you draw a simple ASCII diagram of how things are
    hooked up now?

    And, FWIW, the "tail" and "stop" light arrangement is pretty much the same
    as we do it in the US, and probably most cars around the world; they might
    use different words in different countries, but the effect is the same.

    Sometimes the "tail" lights are called "running lights" which would be in
    parallel with the "parking lights".

    What this leads up to is that there could be a miswire someplace, but to
    really understand the situation I'd need a diagram or something. (I think
    I'm half right-brained. ;-) )

    Good Luck!
    Rich

    Rich
     
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