Motorcycle Accessory Wiring




So you want to run some accessories off of your motorcycle's power, but your bike doesn't have an accessory circuit or anywhere to plug things in? Here are some quick tips on how to do it.

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Step 1: Identify a Circuit to Use

Presumably your motorcycle doesn't have a dedicated accessory circuit, or you'd just be using that. So get a copy of your bike's wiring diagram and find a nice non-critical circuit (just in case we screw things up, we don't want to mess with something that'll stop the bike from running or that'll kill important safety equipment, like brake lights).

Make sure the circuit is suited to your power needs. The wattage that your accessories draw should be well below the power limit of the circuit. For example, if the circuit has a 5A fuse on it, make sure you are using considerably less than 12V * 5A = 60W. Keep in mind that you have to add up all of the draws (including the ones that were on the circuit before you start adding accessories). Don't cut it close. Don't replace the fuse to allow more current.

My bike has a circuit for a light that serves only to illuminate my license plate. Perfect!

After reading the wiring diagram, follow the colored wires to find the appropriate pair. Test to be sure it's the right circuit by unplugging it and seeing what turns off.

Step 2: Get Connectors

This is probably the hardest part of this project: finding the right connectors. You'll probably need two different types: one to interface with the existing wiring in your bike, and another to connect between different accessories.

Why two kinds? Because your motorcycle's existing wiring probably uses something annoying that's hard to connect and disconnect.

I found this connector at a local electronics store. You might also try a motorcycle shop, or an auto parts store. It's handy to take a picture of the connector, because even if you figure out the name of what you want, the person selling them might know them by a different name (like "those black ones with two wires").

I suggest the SAE Connector for the accessory connection end. The plug end has two connectors that fit into each other. One has insulator all the way around it, and the other doesn't. This is handy because your motorcycle's frame is probably grounded to the battery. If a stray positive wire touches the frame, you can make a short. But if you make sure to always wire the insulated end of the SAE connector to power, you don't need to worry about that.

NOTE: One downside to using connectors that already have attached wires is that the wiring colors may be misleading. This is especially true if you're cutting them up and putting them back together in different patterns (like the Y connector in this Instructable), but might even be true if you're using them unchanged. Normally when you wire to power, you use a red wire, and when you wire to ground you use a black wire. But the wires on the connector may not match this. You should use a voltmeter to test which wire is which and mark it. In this Instructable I mark the wires using colored heat-shrink tubing. I always use red for power and black for ground. You could also use colored tape or a marker.

Step 3: Make a Mixed Y Connector

The first thing you want to do is make a connector with one SAE end and two of the matched connector ends. Do this by cutting the matched connector in half, and then join the two ends together facing the same direction. You can be sure the polarities are right in this step by just keeping the colors matched. Red goes to red, Black goes to black.

For the next step, things aren't quite so straightforward. The best thing to do is to get a voltmeter and measure the difference in voltage between the two ends. If it's negative, the wiring is the opposite of what you expect. For example, it happens that the red wire coming out of the connector shown here is actually the ground wire and the black one is the power wire. You'll notice that the original wiring in the bike has entirely different colors (green and brown) so that this confusion is avoided.

Once you've determined which wire is power, slip some red heat-shrink tubing on it. Slip some black heat-shrink tubing on the black wire. That way you know that even if you can't trust the wire color, you can trust the heat-shrink color.

Connect the SAE connector with the correct polarity. Remember: the insulated end goes to power, and the uninsulated one goes to ground. Test this with a voltmeter!

This is a special SAE connector. It has an inline fuse. This is probably a good idea. You don't want a short in your accessory to pull unlimited current.

Step 4: Connect Your Accessories

Now that you have a dangling SAE connector wired into your bike, you can add an accessory. Just add an SAE end to the accessory and plug it in.

Since the power *output* from your motorcycle's power system is on the insulated pin of the connector, the power *input* to your accessory must be on the uninsulated pin of the connector.

Step 5: 12 Volt ("Cigarette Lighter") Socket

Lots of accessories meant for use in cars use these gigantic, silly connectors, so it's handy to have a socket for them...

Because I didn't use colored heat shrink on this, it's a little hard to see, but if you follow the red wire from the fuse, you'll see that it connects to the uninsulated contact of the connector.

PS. You may be thinking: "Hmm. Everything in this system has its own fuse. Isn't that overkill?" Answer: Yes. Each of my accessories started out with an inline fuse. I just didn't bother removing them.

Step 6: SAE Y-Connector

Here's a handy one. If you have just one SAE connector coming off of your bike's power, but you have two accessories, what can you do? Just make a Y-connector.

Again, the only tricky thing here is figuring out which contact is power and which is ground. On the end that you're plugging into the bike, you're connecting to the bike's power (insulated), so you have to use the uninsulated contact. On the ends that you're plugging into accessories you're making power outputs, so the power should be on the insulated contact.

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    16 Discussions


    4 years ago on Introduction

    I have created a kit on my 2012 Road Glide. I connected the wires to the battery terminals and then broke the hot side of the circuit with a fused link and switch. So far I have had no issues other than the wires from the lights getting old and breaking off. It is probably time to run a new set. I would always run a fused link though and go a little under the max rating for your lights. Be safe!


    1 reply

    Reply 3 years ago

    This is an interesting suggestion, but unless you like replacing fuses for fun, I'd reconsider the above strategy. As a rule, you DON'T want an in-line fuse that is LOWER than the that the max current rating of the load. The point of a fuse is to prevent a condition that exceeds normal from causing additional failures - in the above example, you don't want the fuse to blow just because the lights perform within their specified limits (i.e., between min to max). Keep in mind that the max current rating on a load (e.g., lights) is the maximum current that the manufacturer claims the load will draw at a specified voltage - with this information, the user can ensure the power source is capable of providing what the load will need to function as it is designed. Beyond those basic functional parameters lies safety concerns and this is where fusing comes into play. The important factors are what current the wiring, connectors, and any other conductors are rated to carry (and, as eluded to earlier, what the battery is capable of supplying) - you definitely need to ensure that the fuse will fail before the battery catches fire or the wires melt and/or short other circuits.


    4 years ago on Step 6

    great i have done this direct to battery via a relay just wondering where you get your sae connectors

    1 reply

    Reply 4 years ago on Step 6

    Local auto parts stores tend to stock them.


    8 years ago on Introduction

    you shouldnt connect any electrical equipment to your bike like this. check the amps. use a 12volt relay. - adding a pair of fog lamps 110 watt- on a circuit used to power a 5 watt peanut bulb with a 5A fuse - recipe for disaster.

    4 replies

    Reply 8 years ago on Introduction

    yes, a blown fuse every time you want to use them, leading you to put a larger fuse on the circuit. cable that cant cope with the amps that you are forcing down it will melt and or catch light. but then i guess the problem will be solved no more bike = no more electrical disaster.


    Reply 8 years ago on Introduction

    I've added a paragraph about not overloading the circuit.

    If you write up an Instructable on how to wire a circuit using a relay, I'd be happy to link to that as an example of what to do if you have larger power needs.


    Reply 8 years ago on Introduction

    You're right that you shouldn't try to connect a 110 watt draw to a 12V, 5A circuit, since 110W/12V is nearly 10A.

    However, I don't think it's reasonable to say "you shouldn't connect any electrical equipment to your bike like this". I've had this setup going for years, powering GPS units and various electronics. I've never blown a fuse.

    If you're doing something that blows the fuse every time you turn it on (or even occasionally) you should think long and hard about what you're doing. That should be a pretty clear sign that you're asking for more power than the circuit was designed to deliver. The "disaster" you're talking about is the result of ignoring that sign, not the result of wiring into a low power circuit.


    10 years ago on Introduction

    Hi, Aneel! Nice instructable!
    I've a 1980 CB750-F Super Sport Honda, and I added some "fog lamps" the same way You did here.......and realized that It had an"accessory connector" hidden into It's guts (obviously, I found It when my job was done...)

    Also, I noticed a little error in your first photo:
    RED cable is for the positive , aka "power", or "+"
    BLACK cable is for the negative, aka "ground" or "-"

    Anyway, the instructable is clear enough to save our beloved electronics from death!

    2 replies

    Reply 10 years ago on Introduction

    Thanks for your comment.

    Normally, you do use red for power and black for ground, but that connector came with the colors reversed. That's why I put in reminders to test with a voltmeter and use colored heatshrink.

    I've added a note to step 2, explaining the problem more explicitly. Does that make things clearer?


    Reply 10 years ago on Introduction

    Aneel, no puning intended....It was always clear for me (electronic engineer)...It was just "for the kids"  =O)

    Thanks a lot for the info, red rider!