Motorcycle LED Tail Light




If you've been thinking about building an LED tail light for your motorcycle - or any other vehicle - then you need to read this guide. Why? If you're trying to figure out how to do it than you probably have already figured out that LEDs are super bright, turn on and off way faster than incandescent bulbs, and are generally awesome.

Here are a few things to consider before beginning this project. You need to ask yourself if you're up to the challenge. If you have a lot of electronics/soldering/circuit design experience then this is probably pretty simple of a project; however, if you're anything like me I didn't realize how much work I would be doing. Is there any other way to go about achieving the same results? In retrospect, I kind of wish I had just spent the same amount of money to buy an automotive LED tail light off of Ebay and then modified it to fit in my motorcycle's tail light housing.

There are some decent sources out there and I'm certainly not the first person to try and do a build like this but my reasoning behind writing up an instructable is to compile a few of the things that I learned and maybe help make the process easier for someone else who is trying to achieve the same thing.

Step 1: What Do You Need?

Project Cost = Approximately $50. This will depend a lot on if you have any electronics/soldering supplies on hand, if youre willing to order parts online or if you are content forking out more money to buy from RadioShack.

Parts List:
LEDs - $15-$30
Prototyping Board or Perfboard - $5 RadioShack
Solder - Hopefully you already have some.
Jumper Wire - Scavenge if you don't have any readily available. (braided Cat5 would be awesome)
2 X LM317 Voltage Regulator - $1.50 at RadioShack
Various Resistors - A few buck$
Miscellaneous parts including, jbweld, paint, and heatsinks.

Step 2: LEDs

You can kind of pick and choose what type of LEDs you want to get. I got mine off of ebay because they were in my price range and I didnt have to buy too many. After researching a lot I decided that the best solution would be to get the 4-post LEDs. These are the same ones used in automotive applications. I believe the real ones are made by Phillips / Lumileds. You are searching for the term Superflux LEDs. The ones I got were kind of a knock-off but they have awesome viewing angle which works good for tail lights. Make sure that wherever you get your LEDs that you also get all the specs for them. That is the most important part as you will be designing your array and circuits based around their specifications.

Step 3: Running the LEDs

Before you proceed any further Ill have to give a little bit of a disclaimer. The more you start to figure out about LEDs the more you realize that most people arent really running them how they should. LEDs are very sensitive to current and the voltage doesnt matter as much as long as they hit their forward voltage drop so that they will light up. I really wanted to go with regulated current on this project but everything I could come up with was just too expensive or beyond my capabilities. I was able to get some free samples from a company called maxim for some really awesome current regulator chips but they were all surface mount chips and beyond my capabilities. If you think surface mount chips are really cool then you should look at this brochure.
I had luck with getting the company to send me a ton of free samples for many of the chips in there. (Dont abuse) I also considered using a product called schmartboard that claims that it makes surface mount soldering doable. I didnt want to invest in something that ended up not working so I cant say for sure if this option is good or bad.

Step 4: Voltage Regulator

In the end I went the cheap route and decided to regulate using the LM317t voltage regulators that I found at Radio Shack. Here are the things that you must keep in mind when figuring out how to run your LEDs.

What voltage do you want your array to run at? Use this, it will help you visualize too if you are like me and dont have a very extensive background in electronics, series / parrallel circuits, etc.

The LM317 will drop approximately 2V so you need to keep that in mind and make sure your overall voltage will be high enough. Heres my example. I the output voltage to my tail light on my motorcycle and got the following values. When the engine was off each line, tail and brake, output approximately 10V while running would reach upwards of 13V. 10V  2V(LM317) left 8V to power my LEDs. The specs on the LEDs were a forward voltage of 1.9  2.3max. I decided that putting 4 in series would be cutting it too close so I opted for 3 in series so that my array would run at 6V. That gives plenty of juice to run everything and it is easy enough to set the LM317 to output 6V.

Step 5: Wire 'em Up!

Now that you have a plan about how to run your LEDs, you can wire them up. I had this bright idea that I wanted a cool pattern. My array contained 48 LEDs. That equated to 16 series of 3 LEDs all running in parrallel. Once again use as it is really easy to figure this out. Since I wanted to have a cool pattern, my wiring was pretty intense. For the most part I was able to bridge between the posts of my 3 groups with some solder and then for the LEDs that were wired in series but too far apart to just use a solder bridge, I put in a jumper wire. This was pretty simple but then when I had to run 16 different + lines and 16  lines, the whole thing started to get pretty messy.

It would be a lot easier to line these things up so that you could use less wiring and more bridging across the anodes and cathodes of the LEDs themselves. It is probably a lot easier to troubleshoot too if you have a short somewhere. If you do decide to get fancy, just be creative and try not to get a headache.

Step 6: The Math

Once everything is wired up, then 90% of your work is done. You can test out your array using batteries but just make sure that you under run them instead of hooking them directly to 12V and burning them out, that would be bad. The next step is integrating your voltage regulator LM317s.

This site has some information about how to wire these including a table. There are other calculators out there that will calculate the values based on Resistor1 and Resistor2 values. In a nutshell, you follow the wiring diagram on that page or on the back of your Radio Shack package if you bought it from there. You need 2 different resistors to set the output current to whatever you want. Obviously your output is going to be lower than your input  2V for the voltage drop of the LM317 itself.

Step 7: The Circuit

You can view the following circuit that I basically copied for my setup using 2 different LM317s, 1 for the tail light and 1 for the brake. The brake bypasses a resistor to give a higher output current and make it brighter.

It is located about half way down the page but the whole topic would probably be beneficial to read. I left out the diodes which I assume were protection for backwards current into the LM317 but I thought that might be unlikely since the whole array is made of diodes. Who knows though, if you decide to put those in make sure you up your voltage to account for their drop.

(Update) The voltage regulator that provides voltage for the brake lights was getting fairly hot. I heatsinked both of them with an aluminum heatsink and that seems to have helped distribute the heat a lot but my guess is that the voltage regulator is getting 2 X 12V when the brake light is applied. Since the brake light wont ever be applied for longer than a few minutes at a time and it is now heatsinked I think it will be fine. Maybe someone more knowledgeable can explain why that one regulator would be getting so hot. Maybe thats what the diodes are for :)

Step 8: Final Thoughts

That about wraps it up. I used hot glue to secure the board in the tail light, I added two downward narrow viewing angle superbright white LEDs to light up the license plate as the old bulb did that by itself. To secure the heatsinks to the LM317s I used JB weld mixed with some arctic silver thermal grease at about 2:1. I spraypainted the front side of the board a reflective silver color because it was showing up through the tail light. Now it looks more like a light source and not the board inside.

One concern I have is durability and waterproofing. My understanding is that tail light assemblies are normally vented to the elements to provide moisture to get out. That means that moisture can get in. I was going to spray the back with a plasti-dip spray to seal it up but I want to use it for a while to make sure that I dont need to get back at the solder points.

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14 Discussions


8 years ago on Introduction

A future project I have in mind would be to build a Red/Amber LED Matrix display for the tail light and turn signals. Using an Arduino board to program in some quotes for other vehicles on the road. I.E. 'Back OFF!' 'Sorry' 'Thank You' 'Hi!' Really what ever I want, but I will keep it PG. In Texas you can get a citation for offensive gestures/language....


10 years ago on Introduction

In the future, I would recommend using a 78L06, 6V regulator rather than the LM317. Since it's only designed to output one voltage level, it requires far fewer external components (a capacitor is about all you need) and can output up to 1A of current. Basically makes this project a lot easier and a little less expensive.

8 replies


I'd love to build an L.E.D. tail light for our Father & Son build project.

We know "nothing" about "jack", and I was looking for help on this, saw this web site & how your help could make things work.

Would you be interested in helping us then ?

We have a rodio Shack ( "Source" up here in Canada eh ) in our small town.

This build, we are doing is a Bobber XS650, and our Son has fallen in love with a custom tail light & lic palte ubit. "No School" is the maker of it. It has two bulbs, but...... I kind think L.E.D.'s would be way cooler for guys pulling up behind our Son, in their cars :(

Anyhow . . . . just asking is all.
If this would be too much for "US", would it be possible to have some one make us one then ? :)

Thank You,
for your time on this matter, K ?


PS: I don't know how this web site page works, would I be getting an "E~Mial" notice should you reply then ? or do I have to get back on here to read your post ? :( :)


Reply 10 years ago on Introduction

Unfortunately no. When using a voltage regulator, you really have to look at the minimum possible voltage that will be input into the circuit, compared to your target regulated voltage. A higher voltage input is usually okay within limits documented in the spec sheet for the device you're using. In this particular case the author notes that the minimum voltage the circuit will see during operation, which occurs when the engine is turned off, is about 10 volts. Due to the fact that regulators drop some amount of voltage (~2 to 3 volts depending on the particular device being used), we can only regulate the voltage level to an amount 10 volts (minimum input) minus that 2 or 3 volts, which brings us to around 7 or 8 volts to be used in the circuit. In step four the author had reached this conclusion, and decided to optimize the circuit for 6 volts operation. More voltage might be nice, but the author opted for a properly regulated voltage level instead (resulting in a more stable circuit overall). Hope that clears things up. If not, let me know, and I'll try to explain it a bit more clearly.


Reply 10 years ago on Introduction

Thank you. It's been about 15 years did I did anything with electronics and my memory is a bit rusty. I didn't even think of the minimum input voltage.


Reply 10 years ago on Introduction

No prob. Are you getting back into electronics then? I hope so. The basics are always the same. I bet it's like riding a bicycle. You'll begin to remember more and more, and have a good time.


Reply 10 years ago on Introduction

Right on, I was just about to explain that but you probably did a better job than I could. I'm interested to know about the 78L06 chip you mentioned. Since I did this project I have sold the bike but I'm sure I'll do another, better led tail light build in the future as it was a lot of fun.


Reply 10 years ago on Introduction

Actually, the 78** series is one of my favorite IC families, they come in 5v 6v 7v 8v 9v 10v 12v 15v 20v and 24v flavors, generally named 7805 7806 7807 7808 7809 7810 7812 7815 7820 and 7824 respectively. Different manufacturers use differing naming schemes, but those numbers will generally be in the manufacturer part number. I've found these regulators to be very reliable and they require an absolute minimum of external components (a couple caps). There's a pretty good FAQ about the 78** family here: and the schematic at the following site will show just how simple they are to use:

The only real drawback to this type of regulator is that they are intended to output only one voltage level (though this can be tweaked a bit with some wizardry that's beyond the scope of this discussion. see the datasheet. Here's one for Fairchild's variation on the 78 family: ). But if the majority of your work involves only one or two voltage levels (I use 5v and 12v most frequently), then they're a great investment, and very handy to have around.


10 years ago on Introduction

That link to the circuit is down... To confirm, you're running 2 regulators in paralell, and one runs a high resistor after to run dim mode, then the other is 'past' the resistor allowing for the higher non-dropped voltage? COOL.

1 reply

Reply 10 years ago on Introduction

Yeah, that's about it. I just checked that site and it works for me. Check again, I'm to lazy to draw up the circuit but someone did it there.


10 years ago on Introduction

looks good, and much brighter than the pics make it look when you watch the video. (i thought the pics looked a bit dull, but the video made it clear) i'm guessing the brightness drop when you apply the brake in the video is because the camera starts to automatically change it's aperture? also my two cents on the waterproofing: why not wrap it in gladwrap/clingfilm/whatever it's called in your neighbourhood in the interim, to prevent water getting to it, while you're ensuring everything is fine, then waterproof it thoroughly at a later date?

1 reply

Reply 10 years ago on Introduction

Yeah, you're right about the camera aperture. You can see especially on the closeup that it goes bright and then dulls away. The pictures are more dull because I'm running them off of about 4V battery power. It took some playing with and trying different resistor values on the voltage regulators to get the final brightness levels. That's a good idea about the cling wrap. I could wrap it and then tape around the edges with electrical tape or something. Luckily I'm a wuss and I don't ride very much in the elements but I do live in Oregon where it rains pretty much every day. :) Thanks for the feedback.