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Motorcycle Wiring How-To
Wire your bike!




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Wiring How-To

How Much Power Do I Have?

Before mounting any accessories you have to understand how much power your motorcycle's alternator produces and how much of that power is available for use.

Every bike produces a different amount of power and each bike needs a certain amount of that power to run the bike itself. Once you subtract the amount of power needed to operate the bike from the total amount of power produced you'll have the maximum amount of power available for additional accessories.

You can usually find out how much power is available on a specific motorcycle by checking online forums which deal specifically with that bike. Some manufacturers will release this information but often they only give the maximum power generated and not the amount consumed by the motorcycle's actual operation. Manufacturers may provide this information in amps instead of watts.

Amps are the measure of current and watts are the measure of power. Current is the movement of electrons (like water moving through a pipe). Power is like electrical pressure or how much energy can be produced by pushing water through the pipe. Volts, amps, and watts are all linearly related and easy to calculate. If you have two of the three you can calculate the other.

Since voltage is usually +12V you can calculate watts from amps

WATTS = VOLTS x AMPS

This means that if your alternator produces 60 amps then it can produce (12V*60A) 720 watts (Power/Current Calculator). If you then subtract how much the bike consumes you'll have the number of watts you can use for your accessories.

How Much Power Can I Realistically Use?

Once you know how much power is available for use you'll need to figure out how much power your accessories consume. Most devices will specify the maximum wattage the device uses or the maximum current the device will draw. If the device gives a current just multiply the current value times 12 volts to get the power of that device.

Once you have calculated the maximum power consumption of all of your devices, compare that to what you have available on your bike (Power/Current Calculator).

Wiring Knowledge and Background

When wiring your bike it's important to know what options are available to do the wiring.

Knowing what wiring and which connectors to use is important. You also need to know how to protect against weather, vibration and abrasion. Make sure you pick a wire that is capable of handling the maximum amount of current you are going to be using. A multi-stranded wire is the best to use in these types of applications instead of a solid core wire which is used in household construction. Multi-stranded wire is more flexible, can be routed more easily and handles vibration better than solid core wiring.

The gauge of wire used depends on the amount of current it needs to handle. The gauge number is opposite the size of wire, meaning the bigger the wire the smaller the gauge. It makes sense that the bigger wire can handle more current so that wiring your fuse block, lights and heated clothing should use a 12-14AWG wire. A 18-20AWG wiring would be used for smaller devices like a GPS or radar detector.

You don't want to push the limits of your wiring so always make sure to leave a little head room and play it conservative.

What Exactly is a Fuse?

Fuses are commonly used but rarely understood.

Fuses are rated in amps. If you want to know what fuse to use with an accessory, divide the maximum wattage of the device by the voltage of the bike to get the maximum amount of current the device will use under normal operation. If a device uses 6 watts then it can draw up to (6W/12V) .5 amps. You can then use this value to select a fuse for that device. Typically you are going to use a fuse that is slightly more than the maximum amount of current the device can pull.

Since our device is normally capable of pulling .5 amps we can use a 1 or 2 amp fuse on that circuit. (Power/Current Calculator)

One myth about fuses is that they are made to protect the device. Although there is some truth to this it is somewhat false information. A fuse only blows because something has happened to the circuit or device to cause it to pull more current than what it is rated for. In this case the fuse blows and disconnects the circuit protecting your power source from supplying too much current. In order for the fuse to blow the overrated current already has to be flowing through the circuit, and/or device, which means the fuse isn't protecting it. The fuse protects the power source by disconnecting the faulty circuit. This works much the same way a circuit breaker would on a cheap power strip.

It doesn't protect your TV. It protects your house from burning down by tripping the little breaker on the power strip.

When connecting a device to your bike you want to make sure that the fuse is located as close to the power source as possible. This is because you are decreasing the odds that a short will happen between the power source and the fuse. If your wiring shorts to ground (the frame, etc.) between the power source and the fuse, then the fuse won't do any good. By only having a small amount of wire between the connection on the power source and the fuse you decrease the odds that it will short out along that length of wire.

A short is more likely to occur after the fuse -- where most of the wires, and devices, are located.

Plan Before You Execute

You may be planning to mount one device or several devices.

The best approach to mounting several devices is to mount one at a time. Keep in mind the other ones you want to mount after that. Take note of what your accessories need (power, audio, etc.) before you select where to mount them. By doing this you can start to think about where you might need to place a fuse block or intercom system. Different bikes offer different locations to mount accessories so do some research to find out what mounting options are available for your bike. Once you've decided where you would like to mount your device, consider testing that location.

If this is your first time mounting accessories don't get discouraged if your first mounting solution doesn't work. Usually you have to try a couple different times to get it right. You want to take into account how to get power and audio to the device safely. You may need to have it visible or reachable while you're riding. You may also need to protect it from wind and weather. After you've considered all these conditions you can try mounting the accessory quickly with temporary wiring and mounting.

Always make sure devices are mounted securely and safely so that they can be tested on a few rides before you commit to specific location.

Once you decided on a permanent location, the next step will be to run power and, if needed, audio to your device. This can be a challenge as you do not want to have any wires rubbing against the bike and you want to avoid pinched wires. Your path may be determined by where you can position your fuse block or it may be dictated by where you can run your wiring.

Once you've found a location for your device and your power source, you're ready to start wiring.

Wire Routing and What to Look For

When routing wires you want to take into account moving parts, pinch points, crush points, vibration and weather conditions.

Sounds virtually impossible to avoid on a bike but people do it all the time. Some with more success than others. Missing something here will most likely cause one of two things to happen.

One, your wiring is cut and the power to the device is cut off. This is normally called an 'open' and is the safer of the two failures. The other possible failure is a short if there is a fuse in the circuit. If there is no fuse between the short and the power source it will start melting the wiring. One short provides a high amount of current in a short amount of time. This increased current blows the fuse.

A short typically happens when the power wire for a device comes in contact with ground or a heavy piece of metal (like the frame). The wire was most likely pinched or rubbed to the point that the insulation becomes compromised and allows the wire to come in contact with ground.

There are ways to prevent either of the two above scenarios from happening.

Wire loom comes in a few different forms and protect the wiring from abrasion. There's split loom, spiral wrap, expandable loom or braided sleeving, and vinyl tubing. Split loom is probably the most common and is easy to use. It is split lengthwise so wire can be inserted starting at any point along the loom. Spiral wrap is good if you have a bundle of wires that can't be contained within split loom or if the wiring bundle has things sticking out of it like in-line fuse holders or other connectors. Expandable sleeving is also great, looks clean, and is easy to use. However it has a bit of a drawback. Once you've run it that's pretty much it. If you need to run another wire through it or repair something later you have to pull it all out. It looks cool, though, when you get it installed.

Split loom expandable sleeving is also available but it's still a bit of a pain to modify once in place. Finally vinyl tubing is typically what manufacturers use when constructing wire harnesses. Unfortunately once it's made that's pretty much it. However, it is very durable and you have a really clean looking solution once it's installed.

Making Good Connections

Connections are good and bad.

You need them but you want to make sure that you use as few as possible if you can. Every time you make a connection you get two things: a connection and a problem. A connections by its nature is prone to failure from corrosion or poor conductivity. Make sure when you make a connection that it is solid and protected as much as possible. This may mean adding heat shrink to crimp connectors or adding dielectric grease to connections that may be exposed to moisture. Double check connections and make as few as possible.

Using the right tools, the right connectors, and the right wiring will ensure your electrical stays in working order.

Crimp Connectors Drool

Crimp connectors are easy to use and easy to get but are tricky to do correctly.

These types of connectors come in a few different sizes for different gauges of wire. A good crimping tool is something that can be picked up at a local hardware store although better ones can be purchased through specialty supply stores and web sites.

The toughest part about crimp connectors is ensuring that the crimp has sufficiently clamped the wire. You want the wire to be secure and the insulation to be touching the barrel of the connector. Adding a small amount of solder to the connection and adding heat shrink to the connector will help protect the connection.

Locking Connectors Rule

If you haven't heard of Posi-Locks I highly recommend you consider using them instead of twisting or soldering a butt joint together.

These little miracles make it easy to connect wires securely and reliably. The great thing about them is they are easy to install and easy to remove if you decide to do something else with the connection later. I keep a couple of each size in my tool kit on the bike for emergency repairs.

Posi-Locks work by removing the caps on either end and threading the stripped end of a wire through each cap. Then, by screwing the caps down, secure each wire to the posi-lock pressing the wires up against a conductor in the center of the posi-lock. If you decide later that you want to change the connection or solder it you can simply remove the posi-lock by undoing the caps.

Another great feature is that they are reusable. I think they are about the best thing since sliced bread for wiring.

Wire Taps

Sooner or later you're going to need to get power from an existing wire on your bike.

If you can get a connection from a connector without having to tap a wire that's usually the best but sometimes there are no alternatives. Most often people need to tap into a wire to get a switched power source (meaning a wire that has 12V on it) when the bike is turned on.

There are a few ways to do this and most people use a scotch lock type connector. These types of connectors actually slice the insulation and possibly some of the stranded wires to make a connection that is then passed onto another wire that you run to what you want to power. These types of connections tend to be pretty unreliable and fail after some time. They can also permanently damage the wire and insulation which isn't something you want to do to your bike's wiring.

Posi-Lock makes another device called a Posi-Tap that is a much better, more reliable way to tap into a wire.

This little device uses a Posi-Lock on one side to capture the wire you want to power with the tapped wire. On the other side it has a cap with a sharp spike inside it that pierces the tapped wire. It punctures the insulation and makes a good connection with the stranded wiring without cutting anything. If you later want to remove it you can simply unscrew the Posi-Tap and then cover the puncture hole with electrical tape or a little silicon RTV. That will make sure the hole is sealed and will not allow moisture to get into the wiring.

The Posi-Taps are great little items and highly reliable.

Adding a Relay (Switched Power)

A relay is nothing more than an electrically controlled switch that allows you to control one circuit by supplying power from another circuit without those circuits being connected to each other.

Normally this is done where you want to supply something that requires juice connected directly to the battery, because of its high current, but you only want that circuit enabled when the bike is on. The relay is an electromechanical switch that allows you to do just that.

It has two components: a coil and a set of contacts. The coil is typically connected to a switched source so that when the bike is turned on the coil is activated. When the coil is activated the contacts close on the relay which will gate 12V from the battery to a device or fuse block. Now any device that is connected to that circuit will be supplied directly from the battery when the bike is on.

The great thing about the FZ-1 is that you only need to find a wire that supplies +12V when the bike is turned on. The FZ-1 does the rest for you.

Before You Power Up

After you have your device wired up double check everything before you apply power.

If you're familiar with using a multi-meter then use it to check your wiring. Make sure that positive is connected to positive and that the wire doesn't touch ground anywhere. You can do this by making a continuity check between your positive wire and the frame of the bike. It should read like an open (infinite resistance). If it reads less than that down to zero than chances are the wire is touching ground somewhere and you'll need to resolve it before you apply power. If you apply power it would blow the fuse if the circuit is fused. That's why you want the fuse as close to the battery as possible. If the short isn't fused then the short will continue to draw power from the battery to ground at a high rate. Does the term welding mean anything to you?

One of the most common electrical failures is connections. Double check all of your connections. Using dielectric grease is a good way to make sure you have a good connection and it also helps prevent corrosion from moisture. You also want to check any wire taps that you've done. Make sure it's solid and free from vibration. Make sure that the tap is not under stress. The wires should be secured but not to the point of stressing the tap which would cause it later to fail.

Make sure you've connected everything properly.

Disconnecting the battery is highly recommended when wiring. When you connect the battery make sure to connect the positive terminal first and then the negative. This will prevent sparks when connecting the battery. Once you've connected the battery you can start checking power. You should be able to see if there is +12V at the constant +12V bus on the fuse block. You can also check the ground with a continuity test.

Lastly, check that the +12V switched comes on when you turn the bike on. When you turn the bike on you should also check your devices. If they are supposed to come and they don't then turn the bike off and recheck everything. You can prevent damaging your devices by using a multi-meter to check the voltage at the power connector for your device. Once you're sure the voltage is correct you can connect your device with confidence.

Once everything powers up correctly you're ready for a test ride.

Recheck and Adjust

You may not want to button everything back up before you take the bike for a test ride.

Once a device is in place, and you've had a chance to ride with it on the bike, you may want to move it. You may also want to check if your wiring has stayed in place or if it needs to be adjusted.

The steering column is a good place for pinch points. Make sure that when turning the handlebars right and left to full stop it does not rub or pinch your wiring. This isn't always obvious which is why I recommend checking wiring on a regular basis. Every time I do maintenance on the bike I tend to go over all my wiring to see if there's something coming loose or starting to wear from a rub spot.

Wiring tends to be an iterative process. You may have to move something around after you have wired it onto the bike. You may have to reinforce your wiring or completely reroute it.

Taking time up front will save you from spending an hour in the dark on the road looking for an issue.

Full Disclosure

If the headings sound familiar it may be that you've seen them somewhere else. Dale Coyner put it in a format that is very presentable and so the outline is from an article in Motorcycle Consumer News which covered all the basics. I used the outline, NOT the article. All of the content here is from my own experience. And, if you don't subscribe to MCN, I highly recommend it.

 

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