Hydraulic brake light switch with reversed switching?

Discussion in 'The Garage' started by LukasM, Oct 18, 2010.

  1. LukasM

    LukasM Long timer

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    Hey guys,

    I am currently adapting the entire front end including the brake system from a KTM 990 Adv to my BMW F650 twin. As it turns out the front brake light switches are switched differently, meaning that the light is always on and when I brake it goes off. Not all that practical as you can imagine. :D

    Not being an electrical expert at all I was wondering how to solve this. Ideally I would simply find a hydraulic switch that works the same way as the BMW, but I have not had any look. The banjo bolt should be M10x1.0 I think.

    Or is there some other trick how to reverse the switching function?

    Thanks for any help.

    Lukas
    #1
  2. concours

    concours WFO for 48 years

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    Normally Closed versus Normally Open.
    #2
  3. BluByU

    BluByU Long timer Supporter

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    If all you want to do is switch the signal, use a relay.

    Assuming the brake light switch is N/O (normally open) and you would like to have it N/C (normally closed) Get yourself a basic 5 terminal single pull single throw relay (available at almost any auto parts store)

    Connect one side of the brake switch to ground B- (Bike frame or engine)
    the other side of the brake switch to terminal 85 of the relay.
    ignition switched (& fused) power to terminal 86 of the relay.
    One wire the BMW brake light switch wires should go to terminal 30 and 87a should be the other.

    When the brake is applied the switch will energies the relay causing the connection between 30 and 87a to open. :deal

    If you have a N/C switch and would like a N/O switch most of the wiring is the same, just switch the wire going to 87a to 87
    #3
    PaulTim2000 and Johann like this.
  4. LukasM

    LukasM Long timer

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    Thanks for the advice guys!

    BluByU, that sounds exactly like what I need. I'll give it a shot, if it works out I owe you a beer if I ever make it to the far side of Endorn's Moon. :beer

    Cheers
    #4
  5. bing

    bing F800GS & WR250R

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    I know this an old thread but I tried the suggestion with the relay and it didn't work for my setup which is a KTM 390 Duke master cylinder. It triggered the relay but still had the brake light off when you pulled the brake on. I tried swapping 87 and 87a as suggested but it no worky??
    #5
  6. brianbrannon

    brianbrannon They'll ride up with wear

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    Is the old switch normally closed?
    #6