Hello there and welcome to the BMW Car Club of America.

If you are a BMW CCA member, please log in and introduce yourself in our Member Introductions section.

Check Brake Lights

Discussion in 'E30 (1984-1993)' started by SPSullivan, Feb 1, 2011.

    • Member

    SPSullivan

    Post Count: 11
    Likes Received:0
    Hello all,

    I have a problem with my 1988 325ic that I'm wondering if anyone has any ideas for. The check brake light lamp (center overhead console) stays illuminated despite the fact that I have replaced every part that I can think of that would cause this problem.

    Replaced so far: 1) brake light switch, 2) check lamp relay, 3) all brake bulbs with correct nickel bases, 4) the check panel itself, 5) all contacts have been cleaned and are corrosion free, 6) all brake lamps illuminate as designed including the third brake lamp

    What am I missing? Has anyone else run into this problem?

    Thanks so much!
    • Member

    MGarrison

    Post Count: 2,842
    Likes Received:144
    • Member

    SPSullivan

    Post Count: 11
    Likes Received:0
    Thank you for the reply. I checked both ground points, removed and cleaned all ground wires and the mounting points. Brake lights warning lamp is still illuminated. ... What else is there?
    • Member

    MGarrison

    Post Count: 2,842
    Likes Received:144
    I'm hardly a diagnostics expert, but two other things - a short in the circuit (ie, somewhere in the wiring circuit or some part of the harness; ugh for checking continuity and tracing the wiring), or, though I'd think unlikely, if you replaced the check panel with a used one, possibility both check panels have the same problem? Any other work done that could have somehow affected any part of the wiring shortly before this problem cropped up?
    • Member

    SPSullivan

    Post Count: 11
    Likes Received:0
    Update... Problem Solved!

    I found the problem, on the 325 convertible, the 3rd brake light is externally mounted on the trunk lid which exposes the unit to a lot more moisture than a model with an internally mounted 3rd brake light. The 3rd brake light in the convertible also has a small resistor mounted to a circuit board which is about the size of a postage stamp. I found the resistor and circuit board to be corroded around the solder points and corroded at the contact points of the wires to the board. There are 2 br ground wires and 2 gr/bl wires leading to the board, one each from the wiring harness and then from the board to the light bulb itself. I first tried cleaning the points, scraping the corrosion away with a pick, but the check light remained on. I then cut the wires from the circuit board and used a connector splice to put them together, effectively cutting out the circuit board. VOILA! When tested, the check light comes on as intended, then turns off when the brake pedal is depressed. WOW, exactly as intended! To reconfirm the circuit works as intended, I removed a stop bulb to test that the light would come on for an actual failure. Again, it worked as intended, and extinguished when the fault was corrected.

    YEA! I'm no longer being driven insane by a small red led glaring in my right eye when I'm driving!

    Thank you all for reading this and for your inputs!
    • Member

    Zeichen311

    Post Count: 548
    Likes Received:3
    Congrats on making progress but ... I hope you didn't trash that circuit board yet. I hate to be a killjoy but I promise you it had a purpose, which you have now defeated. (My unsubstantiated but educated guess would be detection of a bulb that has deteriorated but not entirely failed [yet].)

    For a small and simple board, you should be able to follow the traces and sketch a circuit diagram for yourself. Then pop over to Radio Shack (or better, a decent electronics hobby shop) and get the parts needed to construct a replacement. It should cost only a few bucks and doesn't have to even be a board--there's nothing wrong with using discrete components and wires if you assemble them well.

    In your shoes, I would be mildly worried about something else in the lighting or check circuit eventually failing or acting weird, just because some apparently pointless little mystery electro-widget had gone missing. Stranger things have happened.... :)
    • Member

    MGarrison

    Post Count: 2,842
    Likes Received:144
    Glad you found it, talk about a piece of E30 'ic-specific trivia! Not a bad idea from NottheStig there, they musta had some reason or another for it originally.
    • Member

    CRKrieger

    Post Count: 1,616
    Likes Received:20
    I don't think that should be a concern. This little board is only there to precisely balance the brake lamp check circuit. We effectively 'bypass' it when we add more lamps to the E28 (It's a relatively simple task - and a good idea - to put more brake-activated lamps in the vacant rear fog lamp locations.), which reduces the circuit resistance significantly. That means we can have a dead brake lamp but the system will probably not trigger because we'll still have four lamps - one more than the original three.

Share This Page