This is the new and improved version of my original tail light mod. For those who have seen or done the original mod, I think you’ll be impressed with the improvements. I’d like to give a huge thanks to Pete AKA “Hambone” from the VTXOA who took my design and made the first actual working prototype. Since I run aftermarket tail lights, I needed someone with stock tail lights to be the “guinea pig” before I unleashed this on all of you. He agreed and has run/tested the unit for several thousand miles through all sorts of conditions to make sure that no problems arose based on the design. I also want to thank Ken (Guitar4Him) who helped me troubleshoot some problems during the design process of getting this circuit operational.

The original mod gave you red tail lights that made the bike more visible from behind using a single red LED on each side. This new mod uses 24 LEDs for the tail lights (12 on each side). These act as both running lights AND brake lights so you get additional brake lighting for increased safety. To make this version even better, it wires up so that when you hit your turn signal the LEDs will turn off and allow your stock incandescent turn signal to be seen as amber. If anyone has ever seen the Electrical Connection tail light mod, it’s very similar – except theirs costs $50.

When I did my first mod, I shopped around a lot and never found exactly what I was looking for in LEDs. On this project, I teamed up with Custom Dynamics to get the best quality LEDs and components. The LEDs are some of the best and brightest available which means a more visible finished product and they come with a lifetime warranty! In addition, Custom Dynamics put a simple and easy kit together so you can buy all the electrical components from one supplier. This means you save money because you’re not paying shipping on different parts from different places, you get discount prices because they buy the parts in bulk, and you get the convenience of “one stop shopping.”

This mod will work on a wide array of Honda motorcycles with the same stock lights and it can be modified to work on any other motorcycle by making changes to the plexiglass “donut.” The electrical circuit will work on any 12V system (cars, trucks, motorcycles). You just have to modify the “donut” to work with your light housing. It was brought to my attention recently that using this setup on bikes with a single turn signal dash indicator light causes a flicker in the lights under certain conditions. After a short time, I figured out that I had overlooked the problems caused by the single turn signal dash light. This is the exact same problem (on a smaller scale) that occurs when you change to all LED blinkers and need to install diodes in your dash light wiring. So, if you decide to do this project and have a single dash indicator light, then keep in mind that adding a diode kit should be part of your plan.

Required tools/Materials

• 1 small piece of plexiglass at least 3″x6″. Most home stores will sell an 8″x10″ piece for ~$5. I recommend 3/32″ or 1/8″ thick. You can also check picture framing places for scraps and the internet is full of places that sell this as well. I’d check locally first so there’s no shipping costs involved.
• 1″ and 2 1/2″ hole saws
• Drill or drill press
• Clear adhesive silicone (I used the marine version of “Goop”)
• Soldering iron & solder
• Wire cutters and pliers
• Electrical tape or heat shrink tubing – (optional) liquid electrical tape
• Philips screwdriver
• 8mm wrench or socket
• Buy this electrical kit from Custom Dynamics, it contains:
  • 24 red LEDs
  • 1 x 220 Ohm 1/4 Watt resistor
  • 6 x 270 Ohm 1/4 Watt resistors
  • 2 x 3 amp diodes
  • 2 x 10 foot lengths of 22 gauge 2 conductor wire
• (Optional) diode kit for bikes with a single turn signal dash indicator

Process
Making the plexiglass “Donuts”

First, the plexiglass “donuts” need to be prepared for mounting the LEDs. I found the easiest way to do this was to use a 2 1/2″ hole saw in a drill press. This makes 2 nice circles that are about 2 3/8″ around and fit well in the turn signal housings. With the outside of the donuts cut out, use the 1″ hole saw to drill out the middle of the donut to accommodate the stock incandescent bulb. After drilling these you’ll have to cut or sand one edge in order to accommodate the screw tab on the stock lens. Your final product should look like the picture on the right:

If you print the picture on the left at “actual size” then it should come out to scale and you can use it as a template to make sure your “donuts” are the proper size. Keep in mind that these don’t need to be built to exacting standards, the “donut” just needs to fit inside the stock signal lens like the above right picture. You can clearly see the plexiglass in that picture because the protective coating is still on it. When that coating is removed you can barely see the donut.

With the outer and inner rings drilled, you can make your marks for drilling where the LEDs will go. Since you are mounting 12 LEDs in each ring there should be one LED every 30 degrees around the ring. Follow the steps in these pictures to finish the LED holes:

Sketch your own template (left) or print this one (right) – just like the picture above, it should also print to scale

Overlay the plexi on the template

Mark the holes

Drill them out using a 13/64″ drill bit

I got the best results by using a drill press at slow speed and “stepping up” from smaller bits to bigger bits until I got to the 13/64″ bit. Too much bit speed or too big of a drill bit will melt the plexi and could crack it.

With the plexiglass “donuts” prepared you are ready to move on to assembling the circuit itself.

Building the LED circuits
This is the circuit that’s going to be built on the “donuts”:

Don’t be intimidated by this circuit. It’s not nearly as complex as it may seem. The build process breaks it down into manageable pieces. You can see that much of this circuit is redundant so it’s just doing the same thing over and over. Each set of 12 LEDs will be mounted on a single donut. This will yield 2 donuts with 12 LEDs on each when finished. The procedure is broken down for making one donut. When you’re finished you’ll need to repeat the process a second time to make the second donut.

In these pictures you’ll see that my wires are orange and green. This is because I used whatever I had lying around when prototyping. Your kit from CD comes with 10′ long wires which have a black and red wire in each. Use the red for positive and the black for ground when you make yours.

Start out by getting your LEDs installed and soldered in the donut. Each “donut” gets 12 LEDs and the 12 LEDs are broken down into 3 “arrays” (series strings) of 4 LEDs and one resistor each. The “+” signs in these pictures indicate where an array starts and the “-” signs indicate where an array ends. By having 2 arrays end in the same place I was able to ground both with only one wire connection. In the pic below I had just finished soldering the LEDs and was beginning to connect the ground wire (I used green for ground, you’ll be using black). As with all my tech write-ups, CLICK ON THE PICTURES if you need to see more detail!

Simply mount an LED in the donut, CAREFULLY bend the wire leads into shape and trim off the extra. Do the same with the next LED (making sure that you are connecting the short, negative lead from one to the long, positive lead on the other). Then add a drop of solder to make the connection. As I progressed through soldering all the LEDs I used a toothpick to apply some of the adhesive silicone to secure them in place in the donut.

Looking at the pic below you can now see where I’ve added the 270 Ohm resistors in preparation for adding the positive wires as well as how I’ve routed the ground wires around the donut and made connections where necessary.

The last step will be to add the positive wire and double check your connections to make sure everything is wired like the schematic above. When you’re finished you should have something closely resembling the 2 pictures below. Each “donut” should contain 3 “arrays” that each consist of 4 LEDs and one 270 Ohm resistor. These pictures are a little messy because I’ve already coated the connections with silicone to prevent short circuits, but if you click for the larger pictures and look closely, you can see the three 270 Ohm resistors which start each array and the 4 LEDs in series that complete each array.

At this point you should test each donut by touching the leads to a 12V battery (bike or car). Technically you can test using a 9V battery if it’s more convenient, the LEDs will just be a little dim. Dim or bright doesn’t really matter right now, you just want to be sure everything is lighting up and all your connections are good. Remember that LEDs will only light when you apply power across them in the right direction, so when you test them make sure your red wire is positive and your black wire is negative.

Once you have completed all the wiring and connections and you have tested the circuit to be sure it works, take a few minutes to coat and seal the entire thing with silicone to prevent problems like short circuits. I squeezed silicone on the back in a blob and then worked it completely around the connections using a toothpick to get into every little crevice.

Here is a finished, wired, soldered and sealed LED “donut” ready for installation:

Now that you have successfully made one complete “donut” light, repeat the same steps and make the other.

Building the run/Brake circuit
With both LED donuts built and working, you can start building the circuit that controls the running and brake light functions. This is the bottom portion of the above schematic that feeds power to both LED donuts. It consists of 2 diodes and a 220 Ohm resistor.

Take the “donut” you’re going to use for the right side of the bike and cut about 6-8 inches off the end of both the black and red wires. You’ll use this wire to build the run/brake circuit. Cut off more from the right “donut” because it will need less wire than the left one to reach where it’s going. Remember that my wire colors in these pictures won’t match yours because I used whatever wire I had lying around. You’ll be using the wire that came with the kit from Custom Dynamics.

Start by soldering the red and black wires each to a diode. Make sure when you solder the diodes that the striped end of the diode is AWAY from the wire. With a diode on the end of piece of wire, you can heat shrink or electrical tape these ends to make sure they are protected against shorting out. Now take the diode that is attached to the red wire and solder the 220 Ohm resistor to the other end (the striped end) of the diode. You should now have something that looks like this:

You can see in the pic above that the stripes on the diodes are AWAY from the wires and the resistor is connected on the striped side of the diode, away from the wire. Once you have this made, go ahead and tape/heat shrink the soldered section between the diode and the resistor to protect it (you can see this done in the picture below).

To make the last connection I recommend cutting your red wire in half and twisting it together with the leftover pieces – the striped end of the diode from the black wire, the unconnected end of the resistor, and the section of red wire you just cut. Put them all together, solder them and you’ll have something that looks like this:

With that completed, tape/heat shrink that last connection and then tape/heat shrink the entire assembly to protect it.

If you look at this setup you should be able to understand how the LED donuts will function as both running and brake lights. Under normal circumstances the LED donuts get power from the running light circuit which passes through the 220 Ohm resistor. The resistor dims the LEDs slightly for normal operation. When you hit the brake, power goes through the other portion of the circuit bypassing the resistor and giving full power to the LEDs. This provides a dim and a bright function in the same LEDs which is perfect for providing both running and brake lights.

With the run/brake circuit and both “donuts” built all the prep work away from the bike is done and you can now move onto fishing wires on the bike.

routing wires
It almost took longer to fish these wires through the turn signal stems than everything else in this project, so I recommend having a friend around to help or at least to calm you down so you don’t destroy the bike, lol… Pull the signal lenses off the bike by removing the one Phillips screw under the housing:

With the lenses off, silicone the donuts into the lens so they’re ready later. Before you do this, it’s important to mention that you should test-fit the “donuts” before adding the silicone (if you haven’t already). Once you are sure the donuts will fit without a fight, clean the inside of the lens well using a little alcohol and allow it to completely dry. Now run 4 little strips of silicone on 4 opposite spots on the lens -you can almost see them in the pic on the left. With the silicone in place, slide the “donuts” into each lens to mount them.

Now set those aside to dry and start getting everything ready to pull the wires.

Look inside the light housing and remove the 2 little gold screws in the back of the housing. These screws hold the bulb assembly in place. With them removed, you can slide this entire assembly to the front of the housing and it will come off the post. Make sure to take out the bulb first!

This is a recycled pic from a different mod so just ignore the LED and wires in the center of the housing

Reach under the fender and remove the 8mm bolts holding the signals to the fender.

Left signal mounting bolt

Right signal mounting bolt

With those bolts removed, there should be enough slack in the stock wires to allow you access to “fish” the red and black wires from the donuts through the light posts (one donut on each side). You will likely need to remove the wires from the “sheath” (the sleeve that covers them) in order to get them through the light posts. Once through, you should be able to slide this stuff back over the wires. I used a small stiff piece of wire (like a coat hanger) lubed with a little WD40 to help get the donut wires through the light posts. I was able to feed this stiff wire from the base of the post (where the stock wires enter) through and into the housing. Once inside the housing, I taped the red and black wires to it and then pulled them back out through the base of the post. Once you get your wires through the post, pull all the extra through leaving only about 3 or 4 inches of slack inside the housing. This 3 or 4 inches of slack should be enough for when you need to replace the turn signal bulb (the extra slack will allow you to remove the lens with the donut and still be able to get to the bulb).

With the wires through the posts, reinstall the signals using the 8mm bolts. At this point it’s probably best to hop over to my article on installing Kuryakyn rear turn signals because the process of routing the wires will be very similar. When running the wires from the back to the front of the fender just follow the course of the stock wires. There are several metal tabs attached to the fender. You can bend these back to get the new wires under them and then bend them back into place to hold the wires. If you are unsure that the wires will stay at any point then just use a zip tie to fasten them to the stock wires. The goal is to get the wires for both the left and right “donut” through the grommet in the front of the fender and to the wire bundle under the right side cover.

The gray wires are the “donut” wires under the fender in this pic

Fender grommet and wire harness under the right side cover

With the wires run and the silicone holding the donuts in the lenses dry you can reinstall the lens and the screw that holds the lens in place. You can see the finished product in the picture on the right. Notice that you can’t see the installed donut through the lens.

Final wiring connections
Now that the LED donuts are made and installed and the wires are routed under the fender, all that is left to do is the final wiring in the wire harness under the right side cover.

Go into this wire harness and find these wires:

• Black w/ brown stripe wire – running lights
• Green w/ yellow stripe wire – brake lights
• Light blue wire – right turn signal
• Orange wire – left turn signal

After digging those wires out of the bundle, get the run/brake circuit you made earlier.

And this is how you’re going to wire everything:

To make these connections you can tap into these wires however you see fit. You can add new connectors or get out the soldering iron and make splices like these. If you’re thinking about using wire taps you might want to read my article on the problems with wire taps and think it over before you make a final decision. Once you make up your mind, these are the connections you’ll need to make:

Wiring for rear running lights mod
LED “donuts”	Run/brake circuit			Bike (under side cover)
		Red input wire	>	black w/ brown stripe wire
		Black input wire	>	green w/ yellow stripe wire
BOTH red wires from the + side of the LED donuts	<	Red output wire
Black ground wire from the left LED donut	<	——————–	>	orange wire
Black ground wire from the right LED donut	<	——————–	>	light blue wire

Those are all the connections. Once complete, you should have a working setup! If you’re unsure how it all works then check this out…
In order for an electrical circuit to work, it has to have power flow through it to ground. The LED donuts get their power from the running light wire which is slightly dimmed by the resistor you built into the circuit. When the brakes are applied, the LED donuts get full power because the brake light wiring bypasses this resistor. Bypassing the resistor gives the LEDs full power which makes them brighten as brake lights should.
Now for the ground – the LED donuts get their ground through the turn signal bulb! The LEDs consume such a small amount of power that when the power runs through the incandescent bulb, it doesn’t cause the bulb to light up, yet the LEDs can still establish a ground through the bulbs. The neat thing about this, and what makes this setup work so well, is that when the bulb does get power (when you turn on your blinker) the lit bulb prevents the LEDs from grounding and therefore makes them turn off.
So those are the basics of how this circuit works and I hope it helps you understand what is happening a little better.

At this point you’re done unless you have the single turn signal dash indicator light as I mentioned above. If you have this problem then check out my article on the diode fix. It will explain why the problem exists and how to fix it for just a couple of bucks.

Finished pictures

After picture – running lights

After picture – turn signal on

That’s it – you’re done – congratulations!

Afterthoughts
This is an inexpensive project when you consider the results. Like I said in the beginning, this mod is similar to the Electrical Connection tail light mod, but cheaper. I can tell you that the pictures here really don’t do this setup justice. They make the LED’s appear much dimmer than they actually are and give the appearance that you only get light where the 12 LEDs are located. In actuality, the LED light disperses throughout the entire lens. The hardest part of this job is fishing the wires through the turn signal posts, but even if you buy the Electrical Connection kit you still have to fish the wires and do the wiring yourself so you might as well save a few bucks in the process. All you need is some basic soldering skill to complete the job and it gives you a much brighter profile from behind which equals a safer riding experience. If you’re unsure about soldering then spend a little time Googling the process. There are a lot of good articles out there discussing the process and explaining the steps in detail. After a little reading, buy yourself a soldering iron and spend some time practicing with scrap wire until you’re comfortable with it. You’ll quickly learn that the process isn’t terribly complicated

This article was obviously written for a Honda VTX with stock blinkers, but since Honda uses these same blinkers on many of their bikes this mod can be easily added to most Hondas (I installed a set on a Valkyrie). Outside of these specific blinkers, this mod can be adapted to work on just about any bike by simply modifying the plexiglass “donuts” to fit whatever blinker housing you have and checking to be sure you attach to the proper wires. The LED circuit in this article is designed to work on any 12V system, so technically you could mount the LEDs to whatever you want and use them for any application you see fit.