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Thread: Parking brake light is buzzing

  1. #1
    Senior Member frederik's Avatar
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    Parking brake light is buzzing

    When I pull the hand brake, the brake warning light turns on continuously (at the top of the oil temp/pressure gauge) and the flasher relay starts buzzing with a fairly high pitch. If I also have the left or right turn signal on at the same time, the brake warning light starts blinking like it’s supposed to.

    It seems to me as if the brake warning light doesn’t pull enough current from the flasher relay to cause it to blink normally. What could be the cause of this?
    1970 2.2S Elfenbeinweiss
    1972 2.4T Targa Aubergine (MFI) [For sale]
    2002 996 TT Midnight Blue
    Member #3833

  2. #2
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    I thought this was normal behavior for that light.

  3. #3
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    I thought some years the brake lit up solid and later years it blinked; which years it changed I do not know ;maybe someone knows?
    1. Chris-Early S Registry#205
    2. '70 911S Tangerine
    3. '68 911L Euro Ossi Blue

  4. #4
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    For a 72, it should blink when the handbrake is pulled or when the indicator is on.

    The handbrake doesn't pull any current unlike the bulbs in the indicators. I would start by cleaning all connections and then try a replacement flasher relay.
    Last edited by 911GP; 09-16-2019 at 10:52 PM.

  5. #5
    Senior Member frederik's Avatar
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    Thanks for the responses. I checked the wiring diagram and the only current pulled when the handbrake is on is through the warning light itself. I know the flasher relay is designed to blink quicker when there is less current, so you can tell whether one of the turn lights is not working. However it seems odd that it would be designed to oscillate so quickly when the handbrake is on that you hear a buzzing sound.
    1970 2.2S Elfenbeinweiss
    1972 2.4T Targa Aubergine (MFI) [For sale]
    2002 996 TT Midnight Blue
    Member #3833

  6. #6
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    Definitely doesn't sound right. Mine flashes at the same blink rate as the indicators. Was it working ok previously or has it always been like this?

  7. #7
    Senior Member frederik's Avatar
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    I only have this car since it came out of restoration about a year ago. The brake warning light didn't work at first, so my mechanic (who did the restoration) connected it with the current behavior as the result. I think a little more work is needed... the buzzing is annoying and I'm also worried that it might cause excessive wear on the flasher relay.

    I'll check the light connections and also what type of light bulb is installed.
    1970 2.2S Elfenbeinweiss
    1972 2.4T Targa Aubergine (MFI) [For sale]
    2002 996 TT Midnight Blue
    Member #3833

  8. #8
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    Here is a diagram of the system. It should blink if the parking brake contact is closed, or if the brake warning light switch on the master cylinder is the problem.
    Name:  BrakeWarning.jpg
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    E Sully
    1973.5 911T

  9. #9
    Senior Member frederik's Avatar
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    Problem finally solved! I had the wrong flasher relay. Most relays, like the one I had, go into a faster flashing mode if one or more bulbs are faulty (if not enough current is drawn). The problem is that with the handbrake, only the very small indicator light draws current so the relay things all bulbs are faulty and starts flashing with a very high frequency which causes the buzzing sound. Instead, we need a different type of relay that indicates failure via the C connector. One of these is the Hella TBB4 4DB003425 as pointed out to me by 911GP. See also this thread: http://www.ddk-online.com/phpBB2/vie...hp?f=9&t=63848

    Unfortunately this relay is no longer available and its replacement has the "faster flashing" error mode which doesn't work. After trying various options, I finally ordered a different flasher relay via parts-wise.com. I don't know who makes it; it is simply marked with the part number 91461830311. But it works! Finally I have a non-buzzing handbrake. The brake light flashes around twice the rate as the turn signals which is fine by me. Hopefully this information is helpful for others here!
    1970 2.2S Elfenbeinweiss
    1972 2.4T Targa Aubergine (MFI) [For sale]
    2002 996 TT Midnight Blue
    Member #3833

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