Introduction: LED Flasher (automotive or Motorcycle)

Picture of 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

Picture of 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

Picture of 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

Picture of The Old Circuit

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

Step 4: Re-use the Original Connector

Picture of 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

Picture of 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

Picture of Parts List

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

Step 7: The New Circuit Retrofitted

Picture of 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

Picture of 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

Picture of 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.


admin (author)2009-04-20

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!

scd (author)admin2009-04-21

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

scd (author)admin2009-04-20

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.

dew26m (author)2016-07-25

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?

JohnP460 (author)2016-07-06

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?

scd (author)JohnP4602016-07-06

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 :)

RxE (author)2016-05-26

Sorry I should have uploaded details that I have available

RxE (author)2016-05-26

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 :-)

MarsG1 (author)2016-05-16

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.

scd (author)MarsG12016-05-17

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.

MarsG1 (author)scd2016-05-17

Okay so you're saying this circuit would work on 6v/12v without adaptation ?

My current original relay is dead and I want to replace it, so in the same time I replaced the original bulbs by led bulbs. They consume something like 200mA each but I can adapt this load in case this doesn't work. Thanks I'll try then :)

scd (author)MarsG12016-05-18

I think the flash rate is not very sensitive to the supply voltage, so the circuit should flash at about the same rate @6V as it does @12V. You can adjust the C1 cap to a larger/smaller value to change the flash slower/faster rate to your liking. What type of LEDs are you using?

a) If you are rolling your own, then a 6V LED supply is OK since a typical red LED only needs about 2V to turn on. Make sure you use the correct resistor in series with the LED to limit the current otherwise you will burn up the LED.

b) If you are planning to use pre-packaged automotive-bulb-replacement type LEDs that are designed for 12V systems, then they may not turn on @6V (or be too dim).

MarsG1 (author)scd2016-05-18

I am using pre packaged led bulbs 6v (yes yes, it exists, Itested them). At first I adaptated the load with power resistor (one for each led bulb) but turns out my relay might be dead (it blinks one time when I turn it on on either side then goes back to no light and doesn't move again). So I'm looking for a solution which would work (whether I remove or not my adaptative loads). I'll try that and we'll see !

MarsG1 (author)MarsG12016-05-18

By I tested them I mean that they are brighter at 6-7V than the 12V-designed that I tested which need more voltage to make a decent light.

MarsG1 (author)2016-05-16

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.

Juan PabloI (author)2016-02-02

Very nice and many thanks it really eorked great with a minimal changes in the resistances actually this never fail and worked so clean in comparison with 2 other I bought from e bay and they last only 2 months. I will attach a final pic.

munish4u911ex (author)2015-09-14

My bike flasher unit is having two terminals only. What do you suggest? I had made something like in the image attached with a 12V relay, but its flashing rate is noticeably dependent on battery voltage. It also stops flashing at, say, 10V, when rear brake light is activated on low battery voltage.

Randy Lahey made it! (author)2015-08-26

My bike has a 2 pin flasher. I modified the circuit to work by putting in a diode. I also used a p-channel fet instead of a transistor (Q1) because that was all I had on hand, so I cant comment directly if this exact circuit will work. But for anyone else considering making can buy one off amazon for about $2 if you don't mind waiting for it to ship from china.

michaelleewebb (author)2012-06-10

hmm, seems your circuit pumps out 85 pulses of power per minute into ground when the bike is on and the turn signal is off. my bike doesn't have the power to spare. could i not place all the 12 volt power lines on the switch except for the 12 volts going into the transistor ?? also a big problem i have is that i turn on the blinker but i forget to turn it off. do you know how to add another 555 to the circuit that would turn off the blinker after 1 minute, even though the switch is still in the on position the blinker stops and won't start again until i turn off the switch and then turn it back on ???

What you need is a 555 in mono-stable configuration mode and then a 555 in a-stable configuration. Basically the mono-stable configuration provides a one shot trigger that powers the a-stable configuration. The a-stable configuration is used to create the actual flashes. The circuit described above is an a-stable configuration. The data sheet for the 555 chip should show you how.

Also, you could use a 556 chip. A 556 is basically two 555 chips in a single package. Another problem is that the mono-stable configuration is designed for a single pulse to trigger it. If your turn signal provides a continual power source, you may have to do some more research. Or you may need to reconfigure your turn signal switch to a momentary switch.

cdickinson2 (author)2015-05-28

C2 acts as a power filter. It absorbs any power spikes. If there is any fluctuation in your power generation, and there almost always is in any vehicle, you will want to have a C2 to filter the power.

anton.beukes.31 (author)2014-11-28

trying to make it, when i get to the red led en connect that to gound it flashes great but when i put the mje2955t and connect no 2 or the collector to a light to test and then the other end to ground nothing. any advice ? coz i just blew 2 555 timers and im trying my best to get this to work

scd (author)anton.beukes.312014-11-28

I'm not sure I can help much (remote debugging is difficult) but check the polarity of your LED. What bulb are you using? The 555 should be isolated from the bulb by the PNP transistor, so I don't know why the 555 would fail when connecting the bulb.

ben_xman (author)2014-01-25

Are there any good alternatives for the MJE2955T? I'm trying to make this out of spare parts and if I could find something else that would work alright that would be great!

scd (author)ben_xman2014-01-26

I think that just about any PNP transistor that can handle the current load will work and if you're just flashing LED turn signals, then the current load will be pretty low (you can measure it for your particular application).

tamasic1 (author)scd2014-09-02

This works very well as a flasher for LED turn signals. I tested it on an old motorcycle with a 6 volt electrical system and it worked perfect. Great project.

ben_xman (author)scd2014-01-26

Thanks! I ended up using a b772 transistor which works! It just gets really hot but it does have a spot to put a heat sink.

kurshiukas (author)2012-04-12

What is the purpose of the power transistor? The original 555 sheet does not include it.

pauldude000 (author)kurshiukas2014-02-22

The 555 timer ic can only source about 200mA of current to a load. Therefore, this circuit uses a 555 to drive a transistor to source up to 10A to power the resistive load of the turn signal bulbs, which can run a couple of Amps.

kurshiukas (author)pauldude0002014-02-28

Understood, thanks!

Janno456 (author)kurshiukas2012-04-14

If you think the on pointed out on my pic, then it's for toggling 12V on & off for you're turn signals. Simply it just acts as a switch thats been trigered by 555 timer output signal.

kurshiukas (author)Janno4562012-04-15

Yes, this one. I just thought that turn switch itself provdes/cuts off current for the cirquit so if your turn switch is on off posittion you do not get 12V to the 1st point of jack and thus the pulsating output is not possible. if you switch it on 12V is provided so it should be possible to use the standart 555 cirquit, or am i missing something?

Janno456 (author)kurshiukas2012-04-15

It depends how is your vehicle turn signal circuit designed. Actually you don't need the transistor, in here it is only used to see if the 555 gives out desired signals. I had 2 wires connected to original relay so I measured which one of them gave out 12V. Finally I connected the 3 first 12V wires from schematic to the one that gave out 12V when ignition was on and the the transistor output wire I connected to the second original relay wire, which took the flashing signal out to my turn signal switch. Ground(-) wire I took directly from my bike battery. Result was exactly the same as with original relay. So when you turn on your ignition the LED D1 starts to blink with mentioned rate and switching your turn signal switch connects the transistor output with signal lights.

kurshiukas (author)Janno4562012-04-16

Got it, Thanks!

ben_xman (author)2014-01-28

I went ahead and sent you a personal message involving a pretty complicated issue that is fairly time sensitive. If you could respond that would be great! Thank you!

lcupu (author)2012-05-15


Janno456 (author)2012-04-08

I made it, tried it and it worked well, except I couldn't get rid off one problem- when I turn on ignition and try my turn signal, it blinks very fast, but after some minutes has passed it works great as it should be. I tryed different capacitors and got some different results: for example using 2.2uF took longer to gain normal flashing rate than using 1uF. Didn't you had this problem, or can someone explayne me why this problem occurs?

tyodz (author)2010-10-28

The instructable is great and would be useful. But it appears that the device will flash continuously even if the flasher switch is in the neutral position. Please correct me if my analysis was wrong. Thanks

abadfart (author)tyodz2011-08-01

well the switch should kill power to the flasher all together

tyodz (author)abadfart2011-09-07

Can you please provide a simplified diagram on how to use this flasher as a direct replacement for the standard flasher. Thanks very much.

Splinter_Cas (author)2009-08-20

Great instructable... will be doing one of these myself.

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