Motorcycle Brake Light Modulator DIY Install

Last updated on December 9th, 2018

Motorcycling is inherently dangerous. And part of that is due to reduced visibility. Everything we can do to tip the scale in our favor helps: high-viz gear, riding with the headlight/high-beam on, loud mufflers… Finally, one thing that can help raise safety via increased visibility is a motorcycle brake light modulator! Especially with drivers who like to get a little too close at red lights. It’s a cheap little device that pulsates your brake light to make it more salient and obvious. Here I’m going to run you through the steps to install it.

Project Specs

Difficulty: 2 out of 5
Tool Requirements: 2 out of 5
Time: 2 Hours
Cost: 2-15$

Just in case how the brake light modulator works isn’t clear

The brake blinker controller works as follows: As soon as you hold down the brake lever (either rear or front), the tail brake light blinks rapidly, then slowly, then stays constant for as long as you hold the brake lever. If you let go of the lever for even a fraction of a second, and press it again, the sequence starts all over again. If you release and press the brake lever within the sequence (while it is still blinking), it also restarts from the beginning.

What does the motorcycle brake light modulator look like?

Brake Light Modulator on a 2015 Kawasaki Ninja 300 ABS

Brake Light Modulator on a 2017 Kawasaki Ninja 650 ABS

What you’ll need

All you will need for this DIY is a GS-100A Brake Light Modulator. “GS-100A” seems to be the generic model number for the part, and a variety of manufacturers make generic versions of it at varying levels of quality. But in essence, they are all mostly the same. All of them will work fine for this motorcycle brake light modulator install.

Motorcycle brake light modulator options

There are versions for “blinking” a single light, or dual brake lights (left and right). You will want to buy the model with two wires coming in, and two coming out. As opposed to “3 in/ 3 out”, or more. Unless you have more than one brake light (like cars). Here are a few redundant links to see what’s available.

Another unit worth considering is the 3rdBrakeFlasher Brake Light Blinker. It’s a high quality, totally waterproof, made in America model. Additionally, it has a lifetime warranty. If you want the best unit, this is probably it. And it doesn’t cost that much more.

Note – Motorcycle brake light modulators don’t like halogen bulbs 

Most brake light blinkers don’t work well with halogen bulbs. The bulb can’t turn on and off quick enough to keep up with the brake light modulator. If you are doing this install on a bike with a 1157 bulb (many Kawasaki and similar bikes), I recommend the JDM ASTAR 1157 Red 5730 24-SMD LED Bulb. I measured that bulb to be almost twice as bright as the stock bulb.

Or, if you don’t want to install an LED brake light bulb you can get a motorcycle brake light modulator like this one. It’s designed to work with halogen bulbs.

Tools

These are the things I used to complete the project. The items within parenthesis are optional, depending on how you do the project.

  • Multimeter – A staple in any automotive electrical project. I happen to be pretty satisfied with this one for quick work like this.
  • Hobby Knife – For stripping wires.
  • (Soldering Iron) – I really like this unit because of the long cable (great for working on vehicles), adjustable temperature, and On-Off switch.
  • (Ratcheting Terminal Crimper) – This is a must-have for professional looking automotive electrical work. It’s the only right way to crimp terminals (which is the right way to make connections). If you get one, make sure it includes multiple jaws. The one I use (albeit a little more expensive – but worth it) is this one.

Supplies

  • (Dielectric Grease) – For protecting electrical connections from humidity.
  • (Rosin Core Solder) – The rosin core helps solder dirty wiring.
  • (Wire assortment) – You’ll want 16 or 18 Gauge wire for this use (around 1 amp for a short distance).
  • (Adhesive Heat Shrink Assortment) – Wire corrosion on motorcycles is a big issue. The adhesive heat shrink helps seal the cable. Needing more than one size for a project is typical.
  • Electrical Tape
  • (Liquid Electrical Tape) – You can apply some of this if you really want to help make the wires corrosion and humidity resistant. It’s a great thing to have in your tool box.
  • (2.8mm 3 Way Connector) – Only necessary if you want to make the motorcycle brake light modulator unit replaceable or removable. For the tiny cost, if you can, it’s worth doing for the saved time later on. I used a 4 way connector in the tutorial since I didn’t have a 3 way at hand. Either would work.

Step-by-step motorcycle brake light modulator installation

Step 1 – Optional: Prep the brake light controller

You can skip this if you simply want to do it the quick and easy way.

Honestly, I’m a fan of “correct” and elegant installations. This installation was made on my new Ninja 650 ABS so I felt like doing it right. That’s why instead of simply installing the motorcycle brake light modulator as is, I did the following. I opened up the little box, connected the two grounds together, (suppressing 1 of the 4 wires) and added a quick disconnect. You can do this too if you feel up to the task, but I recognize it’s unnecessary.

But…why?

Regarding why I did this, the two ground cables are pointless. One is redundant for the vast majority of people. 0 volts is 0 volts, regardless of if that’s at the frame or the negative side of the brake light. At least when working with low potential differences and short distances. So you can connect both negative wires from the controller together. That is, the one going in, and the one going out. In this case I decided to do it inside the little controller’s box, and then encapsulate it again for waterproofing.

Encapsulating the motorcycle brake light modulator…again

After doing the bridging of the negatives, I potted the component again. This is a thermally conductive epoxy which is great for components like this which can generate heat during use.
After doing the bridging of the negatives, I potted the component again. This is a thermally conductive epoxy which is great for components like this which can generate heat during use.

The encapsulation (also known as potting) was done with MG Chemicals Thermally Conductive Epoxy. The stuff is great for protecting electronics from humidity in motorcycle or automotive applications. Especially HID ballasts. It’s the type of stuff that once you try, you’ll find use for elsewhere if you’re an avid DIYer. Just mix the stuff like epoxy and pour it on whatever you want to protect.

If you don’t feel like complicating yourself that much, there is an easier product for protecting electronics from moisture. It’s called a “conformal coating”, which you simply paint on. The one I normally use is MG Chemicals Silicone Modified Conformal Coating. If you want to own just one, the conformal coating is probably more versatile, albeit less protective.

Add a Quick-Connector

After that, if you still want to add the quick disconnect, great. Just crimp on the connections and plug the terminals into the housings.

Step 2 – Locate the tail light brake wiring

I will be doing this installation on a 2017 Kawasaki Ninja 650 ABS. Nevertheless, virtually everything will be applicable regardless of the motorcycle in question. For the most part, it even applies to cars.

The first step is to locate your tail light wiring. On most sport bikes like this one, it will probably be readily visible if you simply remove the rear seat. I removed the left side panel to make things easier for myself. As well as to store the motorcycle brake light modulator there. What you’ll have to move or remove will vary on your bike.

Step 3 – Identify which wire is which

You're looking for two wires. One that is always 0v (respect to the chassis), and another that is around 12v when the brake lever is pressed.
You’re looking for two wires. One that is always 0v (respect to the chassis), and another that is around 12v when the brake lever is pressed.

The brake light will probably have 3 wires coming out of it. One will be ground (permanently at 0v respect to the chassis). Another will be your position light wire (0v at bike off, 12v with ignition on). And the last wire is the brake light wire (12v when either brake lever pressed, 0v if not).

To measure this, unplug your brake light (there should be a connector somewhere near the brake light. Follow the wiring) and measure the voltages on the connector. You only need to find two wires – Ground and Brake Light.

Ground will probably be black. If you set your multimeter on “continuity”, it should beep (or show 0 Ohms) between ground and any uncoated bolt on the frame. Or your battery’s negative terminal.

Next turn the ignition on. You’ll see that one wire is always 12v. That’s your position light. You can leave it alone.

Consequently, there should be one wire remaining. That is the brake light. Double check it measuring the voltage while pressing and releasing either brake lever.

Step 4 – Cut the wiring and make the connections

In order to make the connections for the motorcycle brake light modulator, you’ll have to “tap” one wire, and cut another.

First, the ground wire. Don’t cut this wire. Simply use the hobby knife to strip some insulation (without cutting the wire!). Then, separate the metal wire strands (poke the point of the hobby knife in the middle, then rotate it) to make a loop. You’ll connect the negative from the motorcycle brake light modulator here. Thread the negative wire from the brake controller through the middle and twist it around making a solid electrical connection.

Next step – Cut the brake light wire

Now, the hard part. You’re going to have the cut the brake light wire. I know it hurts, but your bike will forgive you for it. Eventually. Anyway, I recommend doing this on the pigtail going from the brake light to the electrical connector. That way, if for whatever reason you wanted to leave the bike totally stock, you could simply replace the brake light and remove all traces that it was ever there (electrical warranty work?). Then, remove some insulation off both sides and slip on the heat shrink before making the connections (if you intend to use heat shrink – I’d recommend it, though).

Test the motorcycle brake light modulator!

Before actually making the connections permanent, test the controller to make sure it works. Just in case the wires were misidentified or connected wrong. Just wrap the cable ends together (but make sure they don’t touch each other) to test for a moment.

Once you’ve made sure it works, make the connections permanent, and protect the wiring. If you want, solder the connections. I like to do so to make sure they are reliable, however it requires careful technique. If you aren’t familiar with that, learn more about crimping versus soldering before proceeding. Especially on something as important as a brake light. You should also apply liquid electrical tape where possible, to prevent corrosion. Bonus points if you apply marine heatshrink on top of that.

However, I’d be naive if I didn’t at least let you know that many people (and shops, for that matter) would probably use the cheap and quick option – Electrical Splicers. All you have to do is insert the wire and push in the metal tab with pliers. They work well enough, but are not 100% reliable and are pretty bulky. I don’t love them, but sometimes I use them if the situation is right.

Step 4 – Test it!

The final step is to test the motorcycle brake light modulator. Hopefully, all will have gone well.
The final step is to test the motorcycle brake light modulator. Hopefully, all will have gone well.

And surprisingly, that’s it! Test for functioning, and post an image of your bike below to prove you did it!

And you’re done!

The only thing left is to grab a beer 100 miles away to test it out...
The only thing left is to grab a beer 100 miles away to test it out…

Anyway, thanks for reading my guide! Check out the homepage to see what other projects I’ve been up to — here are some others you might like:

Got any tips, suggestions or questions? Leave a comment below.