I have recently changed my motorcycle front blinkers from OEM to LED ones. I did not add resistors: I just plugged the new blinkers into the on-board computer.

The right blinker is blinking correctly, by correctly I mean the same speed as with the OEM blinkers.

OTOH, the left blinker is blinking too fast when I don't speed up. As soon as I speed up, the left blinker is blinking correctly.

I have checked and it did not seems to be a faulty contact since it works with OEMs.

Could you see any reason for this to happen?

Thanks, .x

EDIT: the left blinker is blinking normally as soon as I speed up, it is not related to the current speed.

EDIT2: captain obvious: there are the same blinkers on the right and left sides.

  • Now you know why the parallel resistors are required -- to increase the load to the point where the blinker is not confused.
    – Dave Tweed
    Commented Oct 1, 2016 at 19:36
  • 1
    See chicagolandmgclub.com/techtips/general/581.html for a detailed explanation of how the old 3-prong relay style flasher units work.
    – Transistor
    Commented Oct 1, 2016 at 19:40

2 Answers 2


As far as I know, automotive-class "blinkers" work as self-timed "multi-vibrator", where the blink time is (somehow) determined by impedance of light bulb. It is very frequent to see on a car when one of its turn bulb (front or rear) is broken, the blinker goes about twice as fast. Your observation also indicates that the blinking speed likely depends on battery voltage, when the bike idles, battery likely goes to 15V. So the LED replacement must provide the same impedance characteristics as the OEM bulb if you want blinkers to operate as before.

  • This is the exact answer I would have posted. The blinker circuits expect a certain load from the light bulb, and if they don't see that load then they will blink faster, indicating that a bulb is burned out. You may be able to trick it by putting a resistor in parallel with the bulb, but I couldn't tell you what value or size.
    – DerStrom8
    Commented Oct 1, 2016 at 22:38
  • I didn't know that the fast blinking was intentional. Thank you.
    – Ali Chen
    Commented Oct 1, 2016 at 22:44
  • Hmm, now that you mention it maybe it's not intentional, it could just be a side-effect. I've always found it useful though -- it tells me when I have a bulb out
    – DerStrom8
    Commented Oct 1, 2016 at 22:50
  • @AliChen Thanks for the answer but should the same behaviour occurs on the right blinker if this is the correct answer? I was expecting two scenarios: either it works fine for both or it blinks too fast for both blinkers...
    – dotixx
    Commented Oct 2, 2016 at 12:38
  • Transistor posted a link to inner workings of vintage control circuit. I don't believe this entire circuit is right, because it would not explain the same rate for emergency blinking, when all four bulbs (in a car) blink together and at the same rate as a single pair. It could be that your vehicle has two blink control circuits, or something. Your info that the blinking rate depends on driving condition (which I speculated as related to battery output level) indicates that the issue is marginal, so small differences might matter. Commented Oct 5, 2016 at 19:31

Bulb resistance is your problem, but physics aside, you have a few options:

1) Purchase an LED specific blinker relay. Google will help.

2) Wire a resistor in parallel with your LED.

3) Purchase LEDs or LED blinker assembly that is labeled as "error free" or CANBUS compatible. These come packaged as the same resistance as a typical bulb.

Edit: My 2c... #1 is easy, but your bike won't be stock. #2 is a PITA, but cheap. #3 is just starting over again.

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