Tag Archives: trailer wiring

Harley CAN-BUS Trailer Wiring

Oh boy. If water cooling weren’t enough on new Harley models, now they’ve gone and added another BMW-like feature. CAN-BUS wiring. (Can an electrically adjustable windshield and integrated caviar cooler be far behind?)

In any case, the introduction of CAN-BUS wiring to the 2014 Harley touring bike line-up has created a lot of concern and questions.


You can still wire up your Harley for a trailer. And it won’t blow up your bike, it won’t trigger fault codes, it won’t transmit data behind your back to executives in Milwaukee who have an itchy finger on the “Delete Warranty” button.

Now, there is a twist. As I’ve written about before on this blog, and probably will again, there are two basic types of wiring setups for trailers, four wire systems and five wire systems. These refer to the number of wires used for your signal circuits and nothing else. A four wire system has one set of lights that function as both brake lights and turn signals. A five wire system has brake lights that operate separately from the turns.

For decades, motorcycles have been set up as five wire systems. Your brake light is a separate circuit from your turn signals. And so, the majority of motorcycle trailers made here in the US have been five wire systems.

Here’s the twist. In 2014, Harley eliminated the separate turn signals on the rear fender of MOST (not all…more on that), of MOST of their touring bike line-up. In the process of doing that, they combined the turn signals and brakes, making most 2014-to-present Harleys a FOUR wire system.

If you’ve purchased one of those little import trailers, you’re in good shape, because most of those trailers have a “flat four” plug and are four wire systems. Install a Harley plug-and-play wiring kit and it will, by default, mimic your bike’s four-wire system and drive your trailer lights without any problem.

Now, what if you have, or are planning to purchase a trailer that has separate brake lights and turn signals? In your case, what you need is a “four to five” converter — pretty much the opposite of what every auto parts store sells. You need to split out the brake light from the turn signals.

Luckily, the  wiring kits I sell have an extra CAN-BUS module option that does just this. It installs along with the other plug-and-play components and converts the Harley four wire system into a five wire system for your trailer. No muss, no fuss.

Now, I mentioned that most 2014+ Harleys have gone to this new setup. But there’s an exception. Any CVO model touring bike that has a set of separate turn signals down around the brake light are still set up as five wire systems. That means, when you want to connect to a five wire trailer, you need to do nothing other than buy the standard wiring kit. It will work, by default, with your five wire trailer. To connect to a four wire trailer, you’ll need a five to four converter, just like all the previous Harley models.

I realize that’s all a lot of information and some of it may be confusing. So don’t hesitate to ask for help to get the right kit for your bike. In the end, the thing that’s most important to know is that despite everything you may hear or read about the difficulty of adding a trailer to a CAN-BUS system, there’s really nothing to it. You just need the right kit.

Motorcycle Trailer Wiring Harness for Honda Gold Wing

You just bought a motorcycle camper or cargo trailer and now you need to wire up your Wing. What’s the best way to do it? This video demonstrates how to install the Gold Wing Trailer Wiring Harness on a GL-1800 Gold Wing. This particular kit fits the 2001-2010 model years. The kit for the 2012 installs similarly, but the wiring sub-harness (the first piece you install) connects to different points on the bike.

Trailer and Bike Wiring Compatability

You can connect any trailer to your trike as long as you understand how BOTH are wired.

Q: I am in the market for a good used Escapade in the 1990s and up.

I purchased a 2004 Goldwing Trike last year and am considering now in looking for a trailer although my possibilities of locating one are slim to none because I’ve been searching the web for a year now and still can’t find a good used Escapade for sale.

I was told by the company I bought my trike from to make very sure what kind of motorcycle cargo trailer I ever purchased because all trailer hookups are not the same. For example, if I purchased an Escapade BE SURE the wiring on the trike is for an Escapade; otherwise, it will fry the trike’s wiring.

Can you confirm for me if this is true? Also, are all Escapade models wired the same. Example, I don’t want to have the trike wired for an Escapade LE model only to find out that I found a good deal on an Escapade SE model; however, the wiring is different.

Thanks for your input on both of these questions.

A: Good questions. There is a lot of confusion about bike-trailer wiring, because every company that makes trailers tends to do something different. There are quasi-standards, but no one is bound to follow them. Every maker uses a different style of plug. There are four-wire and five-wire trailers. Four-wire trailers can have five wires, five wire trailers can have six. If you aren’t familiar with them all, it’s hard to sort things out.

First, let me assure you that you can attach any trailer you like to your trike. The key is to understand how the trailer is wired so that you are matching the trike’s wiring to the trailer. This is where some folks get into trouble by matching wire colors, thinking that they should connect “white to white” or “black to black”. That is probably what led to some of those fried wiring harnesses your dealer was talking about.

If you know what light function corresponds to which color wire on your trike, you can match that up with the same light function on your trailer, whatever color it happens to be. If you need to change plugs and slightly rewire the trailer, it’s really no big deal, as long as you know what color corresponds to which light function.

For trailers like Escapade, the company is still in business (and making great trailers), so you can get a wiring diagram with color codes that will tell you what color on the trailer wiring corresponds to the ground wire, brake, turns, and running lights. (While we’re on the subject of Escapade, the wiring for the Escapade LE is the same as the Escapade SE, as the Escapade Elite, etc.)

If you’re buying a used trailer of ANY brand, Escapade, Time Out, ANY trailer, I always recommend that you map which color wire activates which specific light. I’ve seen some that have been rewired over time, and done differently than what came from the factory. I once saw one where it had been completely rewired with ALL RED wire because that’s what they guy had on hand. He made little tick marks on the end to distinguish one red wire from another.

The best way to do this is to simply hook up a 12 volt source to the wires on the trailer and power them up one at a time to see what color wire turns on which light.

If you find your trailer is a four-wire (brake lights operate on the turn signals), you may need to install a 5 to 4 converter so your trike’s brake lights will show up properly on the trailer.

Plugs don’t matter. You can change plugs on the trike or trailer. All you need to insure is that the connection between trike and trailer have enough pins for your wires and stay securely plugged together.

In all cases, I prefer to use an isolating trailer wiring harness for trikes because this powers the trailer lights off of the trike battery instead of adding them to the trike’s signal circuits. If something does happen and a short develops, it will not “fry” the trike’s wiring harness. It will simply take out a fuse on the wiring kit. A fuse that can be easily replaced once the problem is found and fixed.

Good luck in your search – used Escapades are hard to find. When one rider is ready to sell his, he usually has two or three friends in line to buy it. Of course if you decide to go the new Escapade route, feel free to contact me!

BMW CAN-BUS and Trailer Wiring

Question: I’d like to add a trailer to my BMW. I have a 2007 R1200RT. I’m having trouble finding someone who will wire it up. In fact, no one wants to touch it! They say that anything I add to the wiring will cause it to fault and they don’t want to be responsible, etc., etc. Do you have any thoughts or ideas?

Answer: BMW makes a great bike, but in this situation, the wiring system they use for their bikes is a little too smart for its own good. However, it is possible to add trailer wiring to your recent model Beemer. And, as other manufacturers adopt smarter wiring systems, this situation is going to occur with greater frequency.

Most bike signal circuits are wired the way they have been for decades. 12 volt power runs throughout the system and it is applied/removed from lights and turn signals based on the position of various switches, e.g. the ignition switch, kickstand, and kill switch. For the most part, the bike doesn’t monitor the power drain on the system in any way. It either works, or it doesn’t.

BMW began adopting the Controller Area Network BUS (CAN-BUS) for their motorcycles somewhere around the mid 2000’s. It makes sense, and it’s a move that other motorcycle makers will eventually adopt. CAN-BUS is essentially a “smart” wiring harness. It simplifies wiring, which reduces production costs and improves reliability. On the other hand, it makes it difficult to bolt-on goodies that have to interface with the bike in any way beyond tapping the battery. For example, adding a harness to drive the lights on a trailer.

The problem is most apparent when you try to figure out how to make your CAN-BUS bike drive the brake and tail lights of a trailer.

In the department of brake and tail lights, most bikes use a bulb with two filaments, one that operates the tail light and one that operates the brake light. Extending these functions to the trailer is easy. Tap the wiring harness for each light separately and run them to the trailer. Do the same for each turn signal and you’re done.

When you pull off the tail light module of some CAN-BUS Beemers, the first thing you’ll notice is the brake/tail lights use bulbs with just one filament. And just two wires, a hot wire and a ground. How do you get tail lights and brake lights out of a bulb with one filament and just one hot wire? The CAN-BUS system. This intelligent wiring system runs the bulb at a low 5 volts of power, enough to make it glow as a tail light. When you apply the brake, CAN-BUS bumps up the voltage which brightens the bulbs. Voila! Brake light!

This presents two problems for the would-be trailer puller. To begin with, a trailer has separate circuits for brake and running light. Second, CAN-BUS systems are very sensitive to the amount of load on the circuit. Extending the circuit by adding lights can make the bike’s computer think there is a problem, shutting down the circuit. Like I said, a little too smart for its own good, in this situation.

The good news is, there is a simple fix. First, make sure your trailer’s light are drawing the smallest amount of power possible. If your trailer is equipped with incandescent bulbs, replace them with LEDs. Plug-in equivalents that fit standard light sockets are inexpensive. LED lights draw a fraction of the power that incandescents require, which will prevent the bike’s computer from detecting a fault.

Now, since the bike is driving the lights at low voltage, then high, your trailer’s LED lights will mimic the action of the bike. All you need to do is hook up the trailer’s running light circuit to the bike’s combined running light/brake circuit. When first turned on, all your running lights will operate at low brightness, just like they should. And when you grab the brake, your running lights will brighten, just like brakes.

Another option is to use a wiring harness that has been designed for this specific application. I have a BMW CAN-BUS adaptor for single-wire systems that is designed to split out these functions onto two separate light circuits, so you can wire your trailer normally.

CAN-BUS is now appearing on many other bikes, including the most recent Harleys. Soon, it’ll be on just about everything that’s made. But you’ll still be able to wire it for a trailer.

Matching Trailer and Bike Wiring

Question: On the TriGlide hitch you sell, what kind of wiring harness comes with it? My trailer has a round 6 pin plug.

Answer: The TriGlide hitch comes with a five-pin receptacle and plug. This works for most trailers, even those that have a six pin plug. Most motorcycle trailers have four signal wires and a ground wire for a total of five wires. If that’s the case with your trailer, you can use the five-wire harness that comes with the TriGlide hitch, you’ll just need to change the plug on the trailer.

Some trailers come equipped with an extra wire for an interior cargo light. In that case, you can do two things — you can find a six-pin receptacle to match your six-pin plug (not difficult), or you can combine the cargo light lead on the trailer with the running light circuit. This means your interior light will only work if the bike is keyed on, which some folks prefer as a way to prevent leaving the light on and draining the battery.

Whatever the case, you can feel free to change up the plug on the trailer to match up whatever works best on your bike. I talk to some folks who are afraid to change it for fear that something new won’t work, but there’s no magic to the plug that’s on it. You just need to make sure the new plug has the right number of pins to accommodate all the functions on your trailer. Five is usually enough.

Got a question about trailering? Feel free to send it to dale@openroadoutfitters.com and I’ll try to answer as best I can. Thanks!

Wiring Motorcycle Trailer to Work on a Car

Question: Is it difficult to adapt a motorcycle trailer to work on a car as far as lighting goes? I know the trailers are usually five-wire and my car uses four. How does that work?

Answer: It depends. Often it’s not too tricky, but sometimes the setup throws you a curve. The reason a conversion is necessary is because, as you say, a motorcycle trailer usually has five wires and four-wheelers use a four-wire setup. Motorcycles, unlike cars, has a brake circuit separate from the bike’s tail lights. Most cars/trucks have brakes and tail lights that share the same bulbs.

Easiest: If you haven’t yet ordered your trailer, ask your manufacturer if the trailer can be wired for a four-wire system. Some accommodating folks will do this for you just for asking. Put a four-wire harness on your bike, and you can swap the trailer between your bike and car with no conversion.

Simple: If your motorcycle trailer has turn signals with red lenses, you’re in luck. All you need to do is hook up the ground, running light circuit, and two turn signal circuits on your trailer to a four-pin plug and ignore the wire for the brake circuit. This will plug up and work with a car/truck with no problem. You can actually rig up a converter to go between the existing plug on your trailer and a four-wire plug to match the car side without doing any re-wiring on the trailer or your bike. When you want to tow with your bike, just remove the converter.

Less Simple: If your turn signals are amber, you can’t use them as turn and brake. Brake lights must be red. The next simplest thing is to source red lenses for your lights. Many trailer makers use off-the-shelf lights which are available in either color.

Harder, but doable: If you have a trailer that uses proprietary turn signals, like those that match the Honda Gold Wing, you have more engineering to do. That’s because neither the old style (01-05) nor new style (06+) offer tail lights with red turn signals. In this case, you need to do some re-wiring. The easiest way to accomplish this is to move the turn signal wire down, replacing the brake wire on both sides. This is a permanent change, so you’ll want to confirm that by doing this you will still have running lights. You will also need to put a four-wire harness on your bike to run the new system. You are not building an adapter like the “simple” process above, you are making a permanent change to your trailer.

As always, with any wiring project, test your work before you make it permanent, and always do a shakedown run. Don’t do this the night before you take a long trip! If you aren’t comfortable making wiring changes, enlist the help of a buddy from your club or if someone at your dealership is knowledgeable about trailers, ask them for help.

Got a question about trailering? Feel free to send it to dale@openroadoutfitters.com and I’ll try to answer as best I can. Thanks!

Trailer Wiring – Using an Isolation Harness

If you’re starting to think you should forget the idea of trailering to save your bike’s wiring, fear not. Rather than wiring a harness directly, use an isolation harness, also commonly referred to as a relay package. An isolation harness is a simple solution that will not only power your trailer’s lights at full power, it will also electrically separate the trailer’s lights from the bike’s light circuits, preventing any possibility of damage to the bike.

A isolation harness contains a set of relays; one each for the brake, turn signals, and running lights. Your bike is full of relays that control the lights, horn, and many other circuits.  In short, a relay is an electrically-controlled switch.

When installed on your bike, the isolation harness uses your signals circuits as the triggers, but it draws power for the trailer lights directly from the battery.  This means your trailer lights are running at full power and they are separated from the rest of the bike.  Even if a short developed and rendered the trailer’s lights inoperable, it would not affect the bike’s lights.


This plug-and-play isolation harness is for a four-wire trailer and a Harley.

An isolation harness can be installed on any 12 volt motorcycle. A popular relay package I often use has three components: 1) the relay package consisting of a weather-sealed epoxy package with a passel of wires, 2) a 5-to-4 converter package for use with four-wire trailers, and 3) a subharness.

The subharness, consisting of four wires terminating in a four-pin plug, is installed first. If you own an ’88 to present Gold Wing or Harley touring bike you can use a plug-and-play style subharness that plugs into your bike. All other bikes require a universal subharness which contains a set of quick taps. We’ll assume you have something other than a Harley or Wing and need to use the universal subharness because your installation will require a little more effort.

Job one is to identify which wires run your bike’s running lights, left and right turn signals, and brake. If you have added a brake light modulator or other aftermarket accessories, you may already know. It’s times like these that it pays to have the shop manual for your bike or access to an online owner’s forum.

Remove the seat from your bike and look for a wiring harness that runs toward the back of your bike. On many bikes there is usually only one wiring harness running to the lights in the back. Without the shop manual you can still figure out which of those dozens of wires are the right ones to tap. Remove your lights from the back of the bike and make a note of the wire colors for each light. All of your lights should have one color in common and that common color should be the ground side of your wiring. Locate the other color wires in the wire bundle running under the seat. You will need to pull away some of the wrapping around the harness so you can get at enough length of the wires to tap into them.

Before you start tapping, I’d advise that you take an extra step just to make sure you’ve flagged the right wires. Using a pair of pliers, push a straightpin into one of the wires until you’ve punctured the insulation. Attach a test light or voltmeter (set to a range of 20 to 50 volts) with the positive lead on the pin and the negative lead on the negative battery post. Turn on the bike to check the light you’re testing. If you’re checking a turn signal you can expect to see the test light flash on and off just light the turn signal. On a voltmeter, the needle will swing as the voltage on the circuit rises and drops. Do this for each wire and you can feel confident you’ve identified the right wires.

The subharness comes with a set of quick taps. If you haven’t used quick taps before, they’re an easy way to splice in a wire into your harness without actually cutting into your harness. A quick tap has two slots that hold the wire you are tapping and the wire you are adding. Using a pair of pliers, push the metal tab down until it penetrates the insulating jacket of both wires, then fold the plastic tab over the body of the tap to clip it shut. Do this for each of the four signal wires and you have just completed the most difficult part of the trailer harness installation.

After installing the sub-harness, you’ll plug in the 5-to-4 converter if required. You’re probably wondering, “How do I know if I need this?” The easiest answer is to check your owner’s manual or look at your wiring harness.  If you have a separate wire for brake lights and each turn signal, you have a five-wire system. If the wiring diagram in your owner’s manual shows your brake lights combined with the turn signals, you have a four-wire system. This is similar to the wiring scheme used on boat trailers and motorcycle haulers.

If your trailer is a four-wire system, you need to install the converter. Your bike has separate lights for brake and turn signals, so they can operate independently. The converter adapts the bike’s wiring so the trailer’s lights can operate properly, allowing the turn signals to override the brake lights on the trailer. Without a converter, your turn signals will only work when the brake is not applied.

With the 5-to-4 converter in place (or not), you’re now ready for the relay package. The relay has a four-pin connector that plugs into the sub-harness (or 5-to-4 converter), two power leads, and five output wires. Find a spot where you can tuck the relay package. It’s built to be weather resistant but you can usually find one little spot under the seat if you look around.

Next, run the power leads. The relay package uses power directly from the battery to operate the trailer lights.  The relay package contains a set of crimp connections and a fuse to wire to the hot lead of the relay package. Always wire in the fuse! The connectors on the package require a crimp connection. To ensure you get a good crimp, use a real crimping tool to attach the terminals, not a pair of pliers.

With the fuse and terminals wired onto the power leads, connect the relay package to your battery.  Disconnect the negative lead entirely from the battery before connecting the positive lead. This avoids a potentially dangerous situation. When working around the positive terminal, you can’t accidentally short out the battery if the ground lead is disconnected. After disconnecting the ground, connect the positive lead to the positive side of the battery, then connect the negative side, reconnecting the main ground lead.

Before you go further, it’s a good idea to check your work at this stage while everything is easily accessible. Attach a voltmeter or test light to the outputs of the relay package. The ground lead of your test device connects to the ground wire on the relay package. Connect the positive lead of your device to the wire designated for the running lights. Key the bike to the “on” position and check your test device. A test light should simply light up while a voltmeter will read a steady 12 volts on the scale. Check the other lights including brake and turn signals. Make sure the leads of these wires do not contact the ground lead while you are testing.

How did that turn out? Just fine, I’ll bet. Now you are ready to wire on a plug and button up the bike.  I’ll discuss this step in a future installment.

Trailer Wiring – Going Direct

Your trailer’s lighting must be attached to your bike just as you connect a trailer to a car. A trailer depends on the vehicle’s system for power and to synchronize the trailer lights with the vehicle. It was once a common practice to wire the trailer harness directly to the bike’s wiring. This is still a common practice today, but there are a growing number of drawbacks to this approach.

Harley pass-thru connector for direct wiring.

Adding trailer lights increases the load on a circuit originally designed to drive one set of lights. Years ago, that wasn’t an issue. Light circuits used heavier gauge wire and could handle higher loads. Today’s bikes use thinner wire for weight and cost savings. Thin wire has more resistance per foot than thicker wire, so you can expect your trailer lights to receive a lower voltage.

Doubling up the lights probably won’t cause an outright failure, but the wiring harness will simply be unable to deliver the full power both sets of lights require to operate at maximum brightness. When lights experience a voltage drop of as little as half a volt, this can lead to the loss of as much as 20% of an incandescent lamp’s output. That’s a visible difference.

There can be other consequences as well. An increasing number of bikes are sensitive to changes in the load placed on circuits, especially bikes using the new CAN-BUS system like recent BMWs. Wiring in a trailer directly on a CAN-BUS equipped bike can trigger failure conditions in the bike’s monitor systems, even if everything is wired properly. Sometimes it becomes necessary to add countermeasures such as “load equalizers” to make the circuit appear to function normally to the bike’s control sensors. Expect CAN-BUS and other load sensitive monitoring systems to appear on an ever-widening range of bikes over the next few years.

If that weren’t enough, there’s another reason to avoid direct wiring. Even though your trailer may be well designed, the wiring running from the bike to the trailer is exposed to the elements, possible damage, and the potential for shorting. Short circuits and wiring problems are not common, but they can develop over time, particularly at the point where the trailer and bike are plugged together. When a short develops in a direct-wired harness, the problem will affect the bike’s lights as well as the trailer’s.

In the next installment, I’ll discuss a better method for powering your trailer lights using a isolation harness with relays.