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  1. #1
    Senior Member Eddie Loves You's Avatar
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    B&M Cyo dimness w/rear taillight

    Hey guys. I have a B&M IQ Cyo headlight and a B&M D-Toplight XS taillight both powered by a Shimano DH-3D71 dynamo hub. When I plug the taillight into the Cyo the Cyo dims significantly. As soon as I unplug the taillight it is fine. I've traced all of the wires to make sure nothing is shorting and double checked all of the connections.

    The setup didn't do this initially; only for the past few months. I emailed B&M through their website but have not received a response (contacted them a week ago)
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  2. #2
    Senior Member
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    You might be short-circuiting the dynamo through incorrect ground connection. Try to interchange the two wires that you connect to the taillight.

  3. #3
    Senior Member Eddie Loves You's Avatar
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    Like I said I checked all of the wires and connections. When I reverse the wires the headlight will flicker even when it is turned off.
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  4. #4
    Senior Member
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    I have a similar setup on the way. Hopefully, you get it figured out.

  5. #5
    Gear Hub fan
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    Unfortunately electronics can fail. You need to determine if it is the headlight or taillight that is faulty. Beg, borrow or steal another B&M taillight and see if you still have the problem when it is hooked up. If you do it is the headlight, if not then it is your current taillight.

    From the symptom you describe I would guess the taillight is trying to draw way too much current.
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