LED Flasher (automotive or Motorcycle)





Introduction: LED Flasher (automotive or Motorcycle)

I replaced the incandescent turn-signal bulbs in my Kawasaki Concours motorcycle with LEDs because 1) they brighter 2) they last longer and 3) they require less current than incandescent bulbs. Because they require less current, the standard flasher unit (the little box that makes your turn signals blink) senses the low current and thinks there is a bad bulb and it therefore won't function properly. So the standard flasher unit needs to be replaced with one that is compatible with LEDs. You can buy these, but where is the fun in that? I designed a simple LED-compatible flasher circuit and retrofit it into the original flasher case.

Step 1: Locate and Remove the Flasher Unit

First locate and remove the flasher unit. This will be different for each vehicle. Consult your service manual for the location (or listen for the clicking noise when the flasher relay is operating).

Step 2: Remove the Old Circuit From the Flasher Unit

Some flasher units can be disassembled. If you can disassemble it, then by all means do so. In this case they had potted the timing circuit, so I used a hacksaw to cut open the flasher case.

Step 3: The Old Circuit

Here's the old circuit (encased in potting material).

Step 4: Re-use the Original Connector

We'll re-use the original connector and solder our new circuit to it.

Step 5: The Flasher Circuit Schematic

Here's the new flasher circuit schematic. It consists of a 555 timer circuit and a power transistor. The power transistor is probably way overkill, (it is rated at 10A) but it's what I had available. You can vary C1, R1 and R2 for to vary the flash rate and duty cycle. For the R and C values shown, then flash rate is about 1.4 Hz (which is about 85 flashes per minute). There is a ton of information about the 555 timer on the web, including programs that will calculate the R and C values for you.

Depending on the type of components that you choose, the R and C values can vary by 10% or more, so you may need to tweak some values. C2 should be a ceramic bypass cap, but it does not appear to be essential, my circuit worked fine either with or without C2. C1 should be a ceramic cap, but if you decide to use a tantalum or electrolytic cap for C1, then make sure that you install it in the correct polarity, or it could explode. If you have any doubts about your electronics capabilities, then you should not build this circuit.

Step 6: Parts List

Here's the parts list with DigiKey part numbers listed.

Step 7: The New Circuit Retrofitted

I point-to-point soldered the new circuit to the original connector. It's not pretty, but it works. An oscilloscope can be handy at this stage in case you need to debug the circuit. If everything is working correctly the D1 LED will flash at the desired rate.

Step 8: Button It Up

Once everything was tested and working properly, I used epoxy glue to enclose and seal the new circuit into the lower half of the original case. When the epoxy was cured, I re-installed the flasher in my Concours and it has been working well ever since.

Step 9: Voltage Filter Cap Fix for V12V Voltage Ripple Problem

An extra filter cap C3 was needed when this circuit was tried on a 1982 Yamaha XV750 Virago.
The problem was caused by excessive AC ripple voltage on the V12V voltage supply
when the motor was running at over 2000 RPM. The value of C3 is not super critical,
any value around 1000uF should be OK. C3 should be placed as close as possible to U1.

Thanks to Pofarm for testing and verifying this fix.


  • My bike has a 2 pin ...-Randy Lahey

    Randy Lahey made it!


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This is a great Instructable, but you need to add a main image of the final project to the intro step. Please do that and leave me a message when you have so that we can publish your work. Thanks!


I searched for my instructable, but could not find it. Is it published now? Thanks, Scott


I've posted a picture of my Connie, which is where the new LED flasher is installed. It's working great :-) I've also updated a number of the steps with more detail.

What changes would have to be made to use a circuit such as this with standard bulbs and on a 6V motorcycle system with a two-prong blinker relay?

Is this still working long term on your motorcycle? I'm designing a similar circuit, but I was going to use a voltage regulator, PTC resistor, and TVS diode to protect the 555 against voltage fluctations and static which can be pretty extreme, especially on an old motorcycle (I have an old BMW airhead). Is the 555 timer robust enough to handle that?


My circuit is still working, but adding voltage-spike protection is an excellent idea. Once your circuit is working, if you send me your schematic, I will append it to this instructable. Thanks :)


Sorry I should have uploaded details that I have available

Vulcan VN1600 Flasher relay.pngLED 5pin flasher.png

This is very informative for those with a three pin relay :-)

However, I have a five pin relay on the Vulcan Mean Streak,

Purchased a replacement five pin for LED flashers but cannot workout the correct terminal match. If that's at all possible?

Anyone who "knows", I appreciate very much :-)

Hey ! Thanks for the job, great tutorial and very helpfull. I have a few questions to ask you or the community though since I couldn't find my answer on the web.

I'm working on a old motorcycle which uses 1) a very old school relay with a big inductance (magnetic force if you see what I'm talking about) and 2) a 6v voltage. My questions are could I use the same kind of schematic for that bike since I can't modify the current relay and what would I need to change to operate it in 6v ? I can't put the finger on what makes a relay works on 12v or 6v.

Many thanks to whoever will be able to answer to one or both of my questions.


I'm not sure I understand completely, but I assume the relay is not working and you want to remove the relay and replace it with this blinker circuit. If that is the case, then yes, this circuit can work at 6V, but depending on the amount of current your bulbs require, you may need a larger power transistor.