Author Options:

led running brake light circuit for motorcycle? Answered

i want to add 5 LEDs wired for 12 volt in parallel to my motorcycle running lights. then when brake is pressed they will light up brighter. i think i need to add a resistor to each input ( brake and running light wire) to drop voltage down. maybe 9 volts for running lights (which would be on all of the time) and another 3 or 4 volts for the brake light so added to 12 to 13 volts for bright brake lights. any ideas how do i do this and what size resistor i should use or am i looking at this wrong? 


I am adding lights to a sissy bar i made. I thought it would be cool to have the lights always on when my harley is running and when i hit the brakes the lights would get brighter.


OK have you worked with transistors, would you know how to read a schematic?

I haven’t tested this but it should work.
I can test it on a bread board if you like and get back to you tomorrow night if you like.

Break Lights.bmp

Hello Josehf,

this is a great circuit and just i was looking for. thanks for sharing this.

one question though, if i want to increase the number of LEDS, should i just continue stacking them or do i need to adjust for the resistor value?

You can stack a little more but at some point you will need to increase the power of the transistor and the resistor parallel to the transistor.

Thanks Josehf!

all i really need is 8-10 LEDS i hope current circuit would not need to be modified much, just adding a few more LEDS.

At 10 you will need to up the transistor or make two circuits wired in parallel.

OK I built the circuit on a bread board and it worked as planned, so assuming the brake lights on your motor cycle work by battery positive to brake switch to brake light, it should work on your motor cycle also.

I did a component diagram to make assembly easier for you to fallow.

The resistors are six 1 kΩ, ¼ watt, the LEDs I used were five 20 ma brights from Radio Shack and the transistor is a 2N3904.

Just about any small general purpose NPN transistor should do these and the resistors you can get at Radio Shack.

Datasheets you can get from here:

Break Lights.bmp

Thank you very much. I grabbed everything today I would need but was unable to find a transistor at the local radio shack so I ordered on line. As soon as that arrives I will finish wiring and try it out. I do appreciate your help with this. Thank you.I will let you know how it turns out.

Thank you. Worked great. Would this be the same circuit I would use for led turn signals? They are only blinkers but would like to add running lights and break lights.

Finished the sissy bar over the weekend. Everything works great. Thanks. Haventdone anything with turn signals yet. Beings there are three inputs not surehow i would set them up.

Right now the lights are off until the turn signal is turned on and the flash. I would like them on all the time for running lights. Flash for the turn signals and get brighter for brake lights and also brigbter for brakeligbts with turn signal. I ddon't know if it is possible. Each light has 10 leds.

Back signals can be a little more complicated just to be sure what you want the LEDs to do.

10 LEDs each light

LEDs on all the time
Flashes off and on for signal
Gets brighter for breaking
Flashes on and off brighter when breaking and signaling

This circuit should work I will test it on a bread board tomorrow.

For front signal lights the same circuit as the sissy bar.

Break Lights.bmp

The 10 led is in a self enclosed unit. Is there a way to do the whole unit instead ofeach individual led with a resistor?

I think there is What is the current and just to be sure two or three wires and can you post a pic.

I am unable to take a picture of the circuit because it is enclosed in the housing and there is no way to get it out. The current for the running lights run between 4.5 and 6. The flashers about 4.

Thank you again josehf. I will need to collest some of the parts then I will get busy with it.

Do you want the LEDs to be brighter when the break is depressed?
Or do you want the LEDs to remain the same and the break light to come on making the lens brighter?

Search for an LED calculator. That will show you the best way to wire the LEDs and what resistors to use.