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LED interior light problem.......

Discussion in 'A4/S4 forum(B5 Chassis)' started by Nessy, Jan 19, 2008.

  1. Nessy
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    Nessy VW + Audi mad

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    [Jan 19, 2008]
    As I've become bored with the standard yellow-tinged interior lights in my B5 Avant I've changed all the interior lights to white LED bulbs and I have to say it looks very good too........
    However I have one problem that I can't seem to solve.
    The main light unit mounted on the roof consists of 3 bulbs , a middle festoon bulb (the main interior light) and a BA9s bulb (for the map reading lights) on either side....
    The BA9s is a small bayonet fitting bulb, the same as a pre-facelift front headlamp sidelight bulb, except for interior use Audi fit ones rated at 5W instead of the normal 4 watts .
    This brings me to my problem, try as I might I cannot get the LED bulbs in these map reading light fittings to work!
    The central LED festoon bulb works perfectly , but when installed the LED bulbs in the map reading light bulb holders wont work at all.
    Consequently at the moment I have installed the LED central festoon and the 2 old incandescent bulbs, so each time I open a door the light is an odd mixture of pure white and yellow, lol.
    I know LED bulbs are sensitive to polarity but the bayonet fitting bulbs can only go into the bulb-holder one way so cannot figure out why they don't work? I've tried 2 different sets of LED bulbs now from different suppliers with no joy, can any body offer a solution?

    Thanks!
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  3. Randomjim
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    Randomjim Active Member

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    [Jan 20, 2008]
    I recently changed all mine to white led's and i'm glad to hear i'm not the only one to have this problem. Hope someone can help...
    #2
  4. macca
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    macca Member

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    [Jan 20, 2008]
    have you tried reversing the polarity with some wire to see if that works?
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  5. andybnwc
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    andybnwc Member

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    [Jan 20, 2008]
    i have leds in mine and yes if you remove the unit you can bridge the polarity and they work fine and really bright too.... its on a circuit just use a multimeter to find out which one needs swapping
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  6. Nessy
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    Nessy VW + Audi mad

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    [Jan 20, 2008]
    Thanks guys, it did occur to me that if I swapped the wires over on the map reading light bulb holders it might be the solution , I didn't particularly want to do it but it looks as if this is my only option.

    Cheers!
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  7. Randomjim
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    Randomjim Active Member

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    [Jan 20, 2008]
    How easy does the unit come out? Is it just a pull?
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  8. andybnwc
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    andybnwc Member

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    [Jan 20, 2008]
    lens pulls off then 2 small screws at either side if i remember correctly then pulls out .. but dont quote me on that as it was a year ago now and my cars not at hand to look at sorry... but well worth doing
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  9. Nessy
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    Nessy VW + Audi mad

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    [Jan 20, 2008]
    Yep, 2 small self-tappers hold it in , just need to unplug the wiring to the lights themsleves and sunroof switch (if fitted of course,lol) and it comes out .
    Takes about 2 minutes to remove in total once you know what to do......
    #8
  10. docurley
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    docurley Moderator Staff Member Moderator

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    [Jan 21, 2008]
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  11. Nessy
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    Nessy VW + Audi mad

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    [Jan 21, 2008]
    Having spent some time today looking into this, I'm giving up......
    Checked the LED bulbs I have and with a 12v battery discovered that they have the same polarity as the incandescent bulbs which work in the map reading light bulb holder!
    I thought that the problem might have been due to the way the whole courtesy light is earthed but with a test-lead its quite apparent the map reading lights have a good earth connection as it is, why the LED bulbs won't work has therefore got me stumped..........
    Have now sent for some Philips Blue Vision bulbs to go in the map reading lights; it may work or it may still seem yellow; at the moment have nothing to lose by giving it a try!
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  12. andybnwc
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    andybnwc Member

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    [Jan 22, 2008]
    the original bulbs work both ways the leds one way , trust me ive done the swap and works fine , its well worth it
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  13. Nessy
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    Nessy VW + Audi mad

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    [Jan 23, 2008]

    Can I ask how you did it.....
    Took the light unit out of the car yesterday to have a good look at it and also made sure my LED bulbs actually worked by testing them with a 12v battery.....and found that the only way the LED's would work was if the lead (Pb) contact on the end of the bayonet connection was +ve and the metal side of the bulb itself was grounded...
    Thing is, this is exactly the same polarity as a normal incandescent bulb?
    The courtesy light has the +ve supply coming in to the lead contact on the bayonet, whilst the earth connection to the side of the bulbs (all 3 of them) is made from a metal frame that acts as an earth 'bridge' that spans all 3 bulbs.....
    So ,the LED bulbs SHOULD work in the bulb holders, but don't???????
    That's why I'm stumped........
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  14. Randomjim
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    Randomjim Active Member

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    [Jan 23, 2008]
    I also dropped the unit out today and had a look. A picture of how you've done it would be nice :icon_thumright:
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  15. andybnwc
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    andybnwc Member

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    [Jan 23, 2008]
    ok when i get it back i will show you.. if anyone can post a pic it may ring some bells , i remember soldering a piece of cable and bending the circuit too ,i may of earthed onto the main festoon bulb holder, cant quite remember it puzzled me for a while too

    i got a funny feeling i may of used 501 type bulbs instead now sorry
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  16. FactionOne
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    FactionOne Administrator Staff Member Administrator

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    [Jan 23, 2008]
    A little off topic, but I'd be interested to see some photos of the lights in action when they're woking - I quite like the idea of cleaner and more balanced light in mine, I just don't want to do it if it looks too 'cold' (if you see what I mean)...

    Regards,

    Rob.
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  17. Randomjim
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    Randomjim Active Member

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    [Jan 23, 2008]
    Hmm may have to give the 501's a try then. Got loads of them lying around cos i ordered too many lol.
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  18. andybnwc
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    andybnwc Member

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    [Jan 23, 2008]
    yep it defo was 501s cause you can bend the teminals off and solder cables onto them to gain the correct polarity off the circuit board add a little blob of hot glue = spot on
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  19. Nessy
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    Nessy VW + Audi mad

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    [Jan 24, 2008]
    Well, I've managed to get all 3 LED bulbs in the roof light to work!
    Having had a rummage I came upon two sidelight bulb-holders that came out of my pre-facelift headlamps when I converted my car to facelift Valeos last summer.....
    These hold the LED bulbs quite well and have 2 wires trailing from them , so my logic was to install these bulbholders in the light unit instead of doing any major re-wiring of the existing light unit........
    This is where it gets a bit bizarre.
    Off the car, the LED bulb will only illuminate if the end of the bayonet connection is put to +ve and the metal base of the bulb to -ve.
    In situ in the car the LED bulb will only illuminate if the end of the bayonet connection is put to earth, and the metal side of the bulb is put to +ve!
    Work that one out if you can!
    What I therefore did was squeeze the LED and bulbholder into the aperture where the normal bulb goes in the map reading light and fed the 2 wires through to the back of the light unit, the bulbholder brown (ie earth cable ) was soldered to the positive supply from the courtesy light unit , and the bulbholder positive wire was soldered to the earthing bridge piece that spans all 3 courtesy light bulbs....
    I don't pretend to know why, but it all works perfectly, and would be reversible in about 5 minutes should I ever decide to go back to incandescent bulbs in the future.........
    Will see if I can get a pic of the lights in action, so watch this space.......

    [​IMG]

    OK, its not the best pic in the world, but hopefully you get the idea......the light is quite white-blue but as the interior is entirely blue anyway it matches it quite well IMHO...........
    #18
  20. inigoj
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    inigoj Member

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    [Jan 25, 2008]
    I replaced my central light with 12 colour change large 1cm ultra-bright LED's, the soldering was interesting, as i had a job fitting them in the limited space, and i did not want them all to change in sequence.

    It looks a bit chavlike, but is kind of groovy.

    I left the map lights white LED.
    #19
  21. A4_DTM
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    A4_DTM Member

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    [Nov 25, 2008]
    Can somebody tell me please what length is this festoon led and what leds go in doors and in boot where the legs are ?
    #20
  22. andybnwc
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    andybnwc Member

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    [Nov 25, 2008]
    40-44mm long is the one i used , footwells and back pillars are 501s
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