Many riders want to customize their motorcycles with new handlebars. It is one of the first priorities for a lot of riders. The reasons for doing so vary for each rider. There is some commonality though when installing handlebars for everyone. That is the challenge of getting the wiring through the handlebar without damage.
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Damaging The Wires
Damaging the wires is the most common issue for people. Some people try to pull connectors that are too large through the handlebars. Others tug too hard and break connectors. Sometimes the handlebar is the culprit behind the damage. Any of these things can cause damage to the wiring causing a lot of grief.
Handlebar Manufacturer Errors
When companies fabricate handlebars they don't always prep them completely. Some handlebars are curved and made by simply bending the tubing to form the bar. Others, however, have to be welded to create the style of bar they are making. Those weld points are smoothed out on the outside of the handlebar and then painted. Inside the bar though is where the problem often lies. Weld Slag and metal shards at the seam where the two pieces of metal were welded are often left inside the handlebar. This can make it difficult to pull wires through. It can also cut through the jacketing of the wires which will cause short circuits when current passes through the wiring.
Clean The Inside Of The Handlebar
It is a good practice to use a round copper or brass brush to remove slag and shavings inside the handlebar. By attaching the brush to a drill using a long extension you can clean the weld point. Doing this will break apart any shavings and at the same time smooth the tubing of any weld slag that could cause difficulties pulling wiring through. Once the brushing is done, use an air hose or even water to clear out all the debris from within the tubing. Now the inside of your handlebar tubing will have smooth, clean surfaces that won't damage wiring.
Many people now purchase pre-wired handlebars. The manufacturers will pull the control wires through the handlebars and sell them at a heavily marked-up price. It's not necessarily a bad thing if you don't want to attempt wiring them yourself. If you only have control wires purchasing pre-wired bars saves a lot of hassle. The problem arises when you have a motorcycle with a Throttle-By-Wire.
The Twist Grip Sensor
The twist grip sensor that mounts inside the end of the handlebar also has wires. The manufacturer doesn't have your TGS to install for you. Instead, they put a pull string or wire in the bar along with the pre-wired control wires for the TGS. Once you receive the handlebars you still have to pull that TGS through. Now you have to pull it through with wiring already inside. This can be quite difficult and could damage the wires they installed in the bars. It is much easier to pull the TGS wiring and control wiring together at one time. Since you have to pull the TGS wire even with pre-wired handlebars you may as well save the money they charge and pull all of them yourself.
Pull String In The Handlebars
You will need to install pull strings in the handlebars. This can be done easily by tying a small nut to a string or thin wire. Drop it into the end of the handlebar. While turning the bar and using gravity to pull the nut through it will get through to the exit point at the bottom of the handlebar. It may take some shaking and feeding of the string so be patient. You can usually get your pull string through in less than a minute per side. It is also a good practice if you have a TGS to pull two strings on that side of the handlebars. This will allow you to pull each wire harness independently if necessary.
Tying The String To The Wiring
Be sure to tie the string to any wire harness jacketing if it is available. Try not to tie the string directly to the wiring. Doing so could cause the jacketing to pull and leave bare copper. Also, keep from tying the string to any connectors. You don't want those coming off while pulling. Use electrical tape to secure the string to the wiring. Taper the electrical tape at the connectors by wrapping it multiple times to form a cone shape. This will help with pulling it through.
Lubricate The Cabling
You can use a variety of lubrication to assist with getting the harnesses through the handlebars. I use wheel-bearing grease. Petroleum jelly will also work. I have heard of people using baby powder but have no personal experience myself doing it that way. Apply your lubricant lightly from the string about halfway up each wire harness before pulling the wires.
Take your time! You will want to push the wire harness at the same time you are pulling with the string. Depending on the handlebar you may have some difficulty at the sharp corners at weld points. At these junctions push the cable in first until it won't go any further into the handlebar. Then pull gently until it stops. Sometimes you may have to give a strong steady tug to get the wire harness to move. That's ok. Just don't pull so hard that you cause damage to the harness, wiring, or connectors.
Twist Grip Sensor
Once the mechanical part of the TGS begins to enter the handlebar you will want to be careful. If you pull too hard you can damage how the wiring connects inside the TGS. At this point, you will want to push the TGS into the handlebar while barely pulling the string. You will only pull the string hard enough to keep the harness moving through the handlebar until the TGS is seated.
Finish By Installing Controls And Grips
You can install any control housings once the wiring is in the handlebars. It is easier to do this while the bars are off the motorcycle. Also, install the grips. Doing this will give you a completed handlebar to install on the motorcycle. You will still have to add the clutch and front brake once the handlebars are installed on the motorcycle.