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Thread: The *%@#%! brake light bulb warning

  1. #1
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    The *%@#%! brake light bulb warning

    I cant get the stupid warning light to go away and it's starting to get to me. I've replaced bulbs with the new 21watt bulbs and replaced the switch on the brake pedal. Cleaned all the contacts. The only bulb I havent replaced is the small on in the third light (vert). Does anyone know the proper bulb/wattage for there?

    What else should I check!?! Where/what is the control thingy that checks the circuit?

    Side note, the timer on the check panel backlight is AWESOME. just discovered that last night. :-)

  2. #2
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    Download the appropriate electrical troubleshooting manual (ETM) from this site:
    http://www.wedophones.com/BMWManualsLead.htm

    Ensure your lamps in your taillight boards are nickel-based instead of brass. The lamp you asked about on my son's 90 vert is a Sylvania-Osram 921LL. The original BMW part number is 63 25 1 372 632.
    On Christ the solid Rock I stand, all other ground is sinking sand. (Edward Mote 1797-1874)

  3. #3
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    Awesome, thanks! The bulbs are nickel and not brass.

    So.. If I'm reading the diagram right... it really doesnt matter what bulbs are in the sockets, so long as the circuit is complete the check light is satisfied? Since all my bulbs work my check light module must (or one of the relays inside) must be stuck open.
    Last edited by 87iSee; 06-30-2011 at 09:57 AM.

  4. #4
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    richardodn is offline Old Guy BMW CCA Member
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    Not necessarily. If the bulbs pull too much current (i.e. resistance too high), then there is insufficient current to energize the relays. First thing to try is to clean the sockets and connections and replace the bulbs with the correct ones. Even if the old ones are correct, they may now be old. If that doesn't make it go away, the problem may be in the check relay or panel.
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  5. #5
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    Quote Originally Posted by 87iSee View Post
    Awesome, thanks! The bulbs are nickel and not brass.

    So.. If I'm reading the diagram right... it really doesnt matter what bulbs are in the sockets, so long as the circuit is complete the check light is satisfied? Since all my bulbs work my check light module must (or one of the relays inside) must be stuck open.
    The brake warning light is triggered by less than normal current flow through each light circuit. So the bulbs must be of the correct wattage, in good condition, and there can't be additional resistance at the bulb base, socket, or wiring.

    The sensing for the check panel is contained in the monitor module in the left rear fender.
    The car makes it possible, but the driver makes it happen.
    Jim Levie, Huntsville, AL

  6. #6
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    Ah, well that makes sense. The bulbs that came with the car were 26 watt, so I replaced those with the proper 21 watt bulbs. I still have to try replacing the third bulb. I've tried cleaning the all the contacts and they look pretty good. Maybe some electric grease stuff is next.

    Quote Originally Posted by richardodn View Post
    Not necessarily. If the bulbs pull too much current (i.e. resistance too high), then there is insufficient current to energize the relays. First thing to try is to clean the sockets and connections and replace the bulbs with the correct ones. Even if the old ones are correct, they may now be old. If that doesn't make it go away, the problem may be in the check relay or panel.
    Such a touchy system eh. Actually I think the relay unit is under the left-rear seat in the convertibles - according to the manual, ugh

    Quote Originally Posted by thejlevie View Post
    The brake warning light is triggered by less than normal current flow through each light circuit. So the bulbs must be of the correct wattage, in good condition, and there can't be additional resistance at the bulb base, socket, or wiring.

    The sensing for the check panel is contained in the monitor module in the left rear fender.
    Last edited by 87iSee; 06-30-2011 at 10:17 AM. Reason: Automerged Doublepost

  7. #7
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    87iSee,

    I have been through this whole headache with ours, but I stopped short of digging through the wiring harness trying to find the fault.

    All new silver-base bulbs, correct wattage, installed with dielectric grease, two different sets of tail light bulb boards -- and the sutpid light still comes on about half the time when I start it. Occasionally, it will come on when I am driving, and that is when I know that I really need to stop and check the brake lights. You see, I have had one complete brake light switch faiure which announced itself in that way, and I paid no attention -- drove for miles with no brake lights and didn't realize it.

    If I get the "Brake Light Warning" lamp upon start-up, however, I usually ignore it now. I just hit the "Reset" button and the "Check" light goes out; the little red LED light stays on, of course. If I can catch a glimpse of reflected brake light from behind me, so much the better.

    Jeff
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  8. #8
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    Ugh, this is not giving me much hope! There must be a way to fix this. I've never seen the warning light off on my car. I suppose that is better than it only sometimes not working and cause you to wonder about your brake lights! Maybe some slightly lower wattage bulbs, if they exist, would help.

    Quote Originally Posted by BMWtyro View Post
    87iSee,

    I have been through this whole headache with ours, but I stopped short of digging through the wiring harness trying to find the fault.

    All new silver-base bulbs, correct wattage, installed with dielectric grease, two different sets of tail light bulb boards -- and the sutpid light still comes on about half the time when I start it. Occasionally, it will come on when I am driving, and that is when I know that I really need to stop and check the brake lights. You see, I have had one complete brake light switch faiure which announced itself in that way, and I paid no attention -- drove for miles with no brake lights and didn't realize it.

    If I get the "Brake Light Warning" lamp upon start-up, however, I usually ignore it now. I just hit the "Reset" button and the "Check" light goes out; the little red LED light stays on, of course. If I can catch a glimpse of reflected brake light from behind me, so much the better.

    Jeff

  9. #9
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    Have you checked to see all of your brake lights work? Mine was on and it was third brake light. The silly thing is that it wasnt twisted all the way in there.

  10. #10
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    I have. All three are work just fine. Seem equal brightness and all.

    Quote Originally Posted by nightwing66 View Post
    Have you checked to see all of your brake lights work? Mine was on and it was third brake light. The silly thing is that it wasnt twisted all the way in there.
    I FIXED IT!!!! YAY!

    For me, the problem was the third light (mind you I have a convertible).

    First off, I replaced all the bulbs and cleaned the heck out of the holders and the the connections between the bulbs, holders, and wires. None of this solved the problem but turned out to be needed.

    The check relay for the third light is mounted up in the third light unit. You can see a picture of it below. One of the lines on the PCB was damaged (corroded or otherwise broken, see upper left corner of board). I fixed it by soldering in a wire between the leads. As a side note, if you just jumper the two green wires that will bypass the check for that bulb. By fixing the connection on the board my bulb check works properly for all three bulbs!

    FYI, I decided it was the third light as I could hear the relays "clicking" for the lower two lamps. Just unplug all three lights and plug in just one of them. When you step on the brake you can just barely hear the relay click for that bulb if the circuit is working right. When I heard the click for both lower bulbs I knew it was something with the third light.

    Hope this helps someone else!


    Last edited by 87iSee; 11-12-2018 at 11:39 PM. Reason: Automerged Doublepost

  11. #11
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    Quote Originally Posted by 87iSee View Post
    The check relay for the third light is mounted up in the third light unit. You can see a picture of it below. One of the lines on the PCB was damaged (corroded or otherwise broken, see upper left corner of board). I fixed it by soldering in a wire between the leads.

    I just wanted to take a moment and say thanks for posting this. I finally got around to performing this fix and it worked perfectly!

  12. #12
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    Quote Originally Posted by 87iSee View Post
    I have. All three are work just fine. Seem equal brightness and all.

    I FIXED IT!!!! YAY!

    For me, the problem was the third light (mind you I have a convertible).

    First off, I replaced all the bulbs and cleaned the heck out of the holders and the the connections between the bulbs, holders, and wires. None of this solved the problem but turned out to be needed.

    The check relay for the third light is mounted up in the third light unit. You can see a picture of it below. One of the lines on the PCB was damaged (corroded or otherwise broken, see upper left corner of board). I fixed it by soldering in a wire between the leads. As a side note, if you just jumper the two green wires that will bypass the check for that bulb. By fixing the connection on the board my bulb check works properly for all three bulbs!

    FYI, I decided it was the third light as I could hear the relays "clicking" for the lower two lamps. Just unplug all three lights and plug in just one of them. When you step on the brake you can just barely hear the relay click for that bulb if the circuit is working right. When I heard the click for both lower bulbs I knew it was something with the third light.

    Hope this helps someone else!
    Awesome!,
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  13. #13
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    Quote Originally Posted by BMWtyro View Post
    87iSee,

    -- and the sutpid light still comes on about half the time when I start it.

    If I get the "Brake Light Warning" lamp upon start-up, however, I usually ignore it now. I just hit the "Reset" button and the "Check" light goes out; the little red LED light stays on, of course. If I can catch a glimpse of reflected brake light from behind me, so much the better.

    Jeff
    If you are referring to brake light warning on the panel near the mirror, it is NORMAL OPERATING CONDITION for it to come on upon starting the car. It should only go out after you press the brake pedal, thus activating the switch. If yours is only coming on half the time, then you either have a problem or you're stepping on the brake pedal the other half of the time.

  14. #14
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    Quote Originally Posted by 87Cabrio89is View Post

    If you are referring to brake light warning on the panel near the mirror, it is NORMAL OPERATING CONDITION for it to come on upon starting the car. It should only go out after you press the brake pedal, thus activating the switch. If yours is only coming on half the time, then you either have a problem or you're stepping on the brake pedal the other half of the time.
    I did not know that. I thought mine had an issue. I guess I should read my manual? Thanks as that's what mine does.
    2004 S500 4matic w/AMG body kit
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