Motorcycle accessory power. How to add a 12 volt and USB power supply. *Bonus, how to add them to your luggage for long distance travel.

Motorcycle accessory power. How to add a 12 volt and USB power supply. *Bonus, how to add them to your luggage for long distance travel.

Step 1

Know how much power you have to work with. Do the math before you get too deep into adding on more things that could potentially drain your battery. None of your accessories will be of much use if your bike doesn’t have enough power to run them.

For this tutorial, we are working on a [G1] 2nd generation KLR650 that has had most of its lighting changed to LED bulbs. The power supply and usage is as follows:

  • Gen-2 has an alternator or stator that outputs 17 Amps x 14 Volts = 238 Watts
  • High beam headlight uses 55 watts
  • Low beam headlight uses 55 watts (changed to 30 watt LED)
  • Tail Light uses 8 watts (changed to 3 watt LED)
  • High beam indicator 3.8 watts (changed to 3watt LED)
  • Dash lights = 11.4 watts (3x 3.8watt LED bulbs) (Changed to 3 watt LED = 9watts)

ïGen-2 = Standard watts used 133.2. With the LED’s that were installed, only 100 watts.

Additional power used:

  • Heated hand grips 60 watts
  • GPS 10 watts
  • Phone charging 6 watts
  • Tablet charging 10 watts

An additional 86 watts will be used if the bike was to be supplying power to all added accessories that it was intended to run.

With everything requiring power, including hi-beams on, heated grips, and all things charging. We would be drawing 186 watts. The bike puts out 238 watts – 186 watts of maximum draw = 52 watts excess. Great news, we can still add more accessories in the future!

Tools you will require:

  • Automotive grade wire
  • 12V DC relay
  • Crimp-on terminal attachments
  • Heat protecting sheath or flexible sealant like JB Weld 
  • 4”-6” zip ties
  • Screwdriver
  • Crimping tool
  • Needle nose pliers
  • 12V or USB power accessory 

Step 2

There are a few different things you could do here. You could add in a power management tool or an additional fuse box. On this bike, there is not an abundance of aftermarket lights, etc., so we can easily use the fuse box already on the bike. 

  1. First, you'll want your bike on the center stands or a stable lift. Then remove the seat to gain access to the battery.
  2. Next remove the battery ground wire, so as not to cause a short.
  3. In these photos I already had a relay in place for my heated hand grips. If you need to install a relay these are the steps:
  • Find a source of power that is active when the key is on. Use this as your power supply. Then splice in your relay power wire to this power supply. 
  • Attach the crimp on ends that attach from the relay to your power supply in one of two ways. Either solder the wire to the connector, then cover it with heat shield protector sheath. Alternatively, crimp it into place with a crimping tool and seal it to keep out the moisture. In these photos we enclosed the new wiring to the relay with a thick coat of JB Weld. You could also use a flexible silicone-based sealant like clear bathroom caulking. I originally installed the relay with the caulking 40,000 miles ago and have had no issues.
  • Then, wire in your relay according to the instructions. Noting that it only works to displace positive power. Your negative power will still need to run back to the battery.

Step 3

Once your relay is working correctly, attach the power supply from the 12V or USB accessory to the relay then run the negative from the accessory back to the battery. Next, CHECK TO SEE IT IS WORKING. Before tying everything securely in place, you will want to make sure it works. You never know if you bought a faulty product or did something wrong. It's easier to fix now, rather than after you've completed the installation.

Step 4

If everything is working correctly, then find an out-of-the-way place to run the accessory wires. Here I wanted the 12V/USB power supply mounted on the handlebars. I opted to run the wires towards the dash then up to the handlebars. In this situation I needed to remove the fuel tank, you might need too as well. Make sure where you run the wires does not affect the steering, and the wiring won’t be pinched by anything around it.

Step 5

Now that everything is in place test the accessory power supply again to make sure it's working. If it still works, zip tie the wires out of the way. Install the fuel tank or anything else you needed to move. Make sure to secure the connection of the screw into the battery terminals, and install your seat.

 You should now have a fully functioning power supply and be ready to charge or run your accessories like a GPS or cell phone.


As a bonus will explain how to run accessory power to your rear luggage for long distance travel.

For some, it might seem unnecessary to have much more than a place to run your GPS, charge a phone, or possibly operate an air pump in emergencies. For others doing long distance travel with their motorcycle they might need to safely charge items like tablets, cameras, cell phones, etc. while they ride. As many nights on long-distance travel might be spent camping, opposed to a hotel with power to charge up your gadgets. 

For this, the steps are generally the same as above, and I would recommend wiring into to the relay. You don’t want things charging while your motorcycle sits parked overnight.

Decide where you want the power supply based on convenience and how practical it will be to use. Here I wanted the charger in the top box as it was where I carried most of my electronics and the top box is rarely removed.

As an option, you could drill a hole to run the wire through the box, so it is neatly out of the way. For this, you'll probably want to drill a hole slightly larger than the accessory wire, then install a watertight O-ring to keep moisture out. Once the wiring is in place, you might also want to seal it in place with silicone.

On this box I wanted to have the option to easily remove the accessory if I needed to remove the top case (you could cut the wire and add a connector to easily unplug and plug it back in). I also wanted to try it for a few thousand miles before I decided if I wanted to add holes to my box. In this example, I ran it a bit less "clean." 


  1. I opted to trim some of the exterior cover from the wire to make it flat. This accessory power supply had a very durable exterior, close to ½”. I then trimmed it down with a utility knife without exposing the wires inside. 
  2. On the Pelican case top box, I shaved down a space in the watertight seal just big enough to fit the wire in. This shaved area should prevent the wire from being heavily pinched. I then opted to hold it in place with some gorilla tape, as this would also provide a protective spot to wear. I could then also see how much wear was happening. Next, I zip tied as much of the wiring out of the was as was possible, and taped the rest.
  3. On the inside I left about 12” of cord to use in the event I wanted to move the power supply to different parts of the box.

Now that the charger is in place accessories can be securely charged while driving down the highway, and if I choose to move the location or drill holes in the box later. I won't need to make any repairs. 

Things to note

* Your 12V/USB accessory should have an inline fuse. This fuse will save your electrical system in the event of a short. The fuse will blow, opposed to possible your whole electrical system faulting. 

*If you want your power supply to be on full time, wire the accessory power supply directly your battery. Here I wanted my GPS with continual power, so I wired it directly. For the rear luggage power supply, I wanted it only active when the key was on, so as not to drain the battery when the bike was not running. I ran it through the relay I had in place. 

*You will want to add a voltmeter to monitor the power supply of the bike. The voltmeter will warn you of any power supply problems if they should arise.

* Finally, save yourself some trouble. The bike originally had a USB and 12V power mounted above the dash. This location seemed like a convenient place at first. The problem was that due to its location the ports would continuously rattle and in a short time, the USB and several ones to follow would rattle apart. It was also challenging to maintain a stable 12V connection, as it too would rattle out of the hole.