Brake light / indicator problem. - BMW F800 Riders Forum & Registry



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  1. #1
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    Good evening all.

    This is my first post, I do apologise for not introducing myself earlier.

    I’ve had an 2010 F800s for a few months now and she has been faultless until recently.

    When I apply the rear brake both rear indicators light up dimly and the rear brake lights bright no problem. And when I turn on the left indicator for example the right one will dimly shine at the same time so it looks like I’ve got hazards on.

    The front ones work fine no problem.

    I’ve checked and cleaned the contacts but I’m uncertain what I can check next. As far as I’m aware there are no other modifications done to it.

    Any advice appreciated, many thanks.

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  3. #2
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    it sounds like a (possibly) pinched wire, check the wiring under the tail section to make sure some of the wires haven't gotten smashed together. It sounds rather like a high resistance short, possibly caused by the insulation on t adjacent wires being smashed and somehow touch together. Really there's no good explanation without some pictures. It would be almost impossible to troubleshoot it here on a forum like this. You will probably get several answers, and some of the people answering have NO mechanical experience whatsoever. On the other hand are several good mechanics too, don't get me wrong. Best bet, if you're not familiar with CanBus electrics, is to take it to someone who does, and they'll help get it sorted out for you.

  4. #3
    Runmyownlife's Avatar
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    Are any warning indicators displayed on the dash?

    With what seems like an electrical issue, my first thought would be "what do so these have in common?" This is where a schematic comes in handy. I'll look for one.

    In the meantime, without a schematic, try different scenarios and see if there are any deviations. Engine on, engine off (key positioned in "ignition"), weight on seat, no weight on seat.

    These could point to a bad ground, pinched wires, a corroded connector, water, etc.

    My next step (with a schematic in hand, this would be step number 1) would be to trace back (visually at first, then a multi meter) the wires from the rear, to the ZFE and the various switches to the ZFE. (Nothing is direct wired from switch to light.) Again, look for an area where wires from the rear signals and brake lights come together.

    Weird electrical issue very often are related to a poor ground. As you go about the troubleshooting, remove water, clean and tighten as you go.
    Last edited by Runmyownlife; 01-03-20 at 12:17 PM.
    Concrete remains undefeated. 

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  7. #4
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    A bad ground connection is where I would be looking. It is probably around the rear light itself at a guess.
    BMW F800ST, 2010, Black, Fuzeblock, Sat Nav, BMW Tank Bag, Givi Touring Screen, 

  8. #5
    Runmyownlife's Avatar
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    I highlighted an area with a green box and a red circle to show how all these lights are related.

    I'm not sure exactly where this can be located, but as DJ123 suggests, probably a harness near the brake light assembly.
    Concrete remains undefeated. 

  9. #6
    Points: 135, Level: 2

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    Good evening all,

    Thanks for the replies everyone I really appreciate it. I've had a quick play this evening and I think I've found the issue.

    I should have said there were no faults lights and it happened either way when the bike was switched on or with the engine running so I do apologise.

    I disconnected the 5 pin connector for the rear lights and indicators of the bike and sprayed a bit of WD40 on it and that did appear to solve it at first but then I put the seat back on and it started doing it again admittedly the indicators were only lit up faintly but flashed bright when I turned them on.

    So I pulled the seat off again and when I twisted and turned the 5 pin connector whilst it was connected and the indicator lights would brighten and dim as I turned it so I'm assuming I've got a slightly damaged wire going into the connector block.

    So now I'm wondering if its worth trying to salvage the wires or should I try and get a second hand wire harness since at first look they don't look too expensive.

    Many thanks again.


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  10. #7
    Runmyownlife's Avatar
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    The fault likely lies within the 5 pin connector - one somewhat loose wire occasionally and barely making contact with other pins. Keep in mind the fault could be on the male side or the female side. Not sure how serviceable that is; maybe poke around and explore that a bit.

    I'd say good news overall, though. Sometimes finding the problem is the hardest part! Nice work.
    Concrete remains undefeated. 

  11. #8
    Points: 135, Level: 2

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    Good afternoon all,

    Just finished playing with the bike and all is good now.

    I cleaned the connector block with WD40, left it for a while to dry so to speak then connected it and put a bit of wire tape around the wires at the end to restrict any movement / pinching and it works like a charm. The indicators only come on when I want them to now.

    Once again thanks everyone.

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