Time and again, I’ve had people tell me that they are afraid to modify their wiring bike’s harness to install a new accessory. Upon a little digging, the bugaboo is usually fear of splicing wires into the bike’s harness. While cutting your motorcycle’s wiring harness is not to be taken lightly and should only be attempted when you are certain as to which wires should be cut – by, say, obtaining the factory service manual – the process isn’t really that scary.

The source of the splicing fear usually is ignorance about soldering, which apparently many feel should only be done at midnight, during the full moon by a practitioner of the dark arts. Fortunately, that idea is bunk. Anyone, even someone whose hands shake as much as mine do, can learn to solder with a minimum expenditure of blood and treasure.

Turn On: How To Install Switched Accessory Power To Your Motorcycle

wire splicing

The wire tap is evil personified. The piece on the right cuts through a wire’s insulation, possibly damaging the wire strands within. A motorcycle’s vibration can loosen the tap and cause intermittent connection failures or just make it pop off the wire.

The most common connectors you’ll find in aftermarket kits are the crimp-on wire taps. These are tools of the devil. Throw them away and either learn to solder or use Posi-Lock connectors, which are a little more expensive, but I’ve yet to have one fail. With Posi-Lock connectors, strip about a half-inch of insulation from the wire ends but don’t twist the individual strands. Slide the plastic collar over the wire end and then screw the collar and wire into the Post-Lock body to a strong finger-tight. Repeat with the other wire end. This produces a strong, electrically sound joint that I’ve used for years when there’s not enough room to solder. I’ve also used the Posi-Locks as wire connectors in locations where the joint may periodically need to be disconnected.

wire splicing Posi-Lock

A Posi-Lock makes solder-free butt connections reliable and reversible.

wire splicing Posi-Lock

When properly assembled, the butt connection is as strong as the soldered connections shown below. Posi-Taps allow three-way connections.

The reason crimp-on wire taps are evil is pretty simple. While you’d think that they would make splices easy by just clamping into place, they can also cut through some of the actual wire strands, making the wire weaker, higher in resistance, and more prone to failure. Additionally, the high-vibration environment of a motorcycle makes crimp splices more likely to loosen and cause intermittent failures which are a pain to track down.

wire splicing butt

A butt splice is used to connect wires going the same direction.

A decent 40-watt soldering iron can be purchased for under $20, but I recommend one with a variable switch and built-in stand. If you watch for sales, they can be had for $35 or less. You want some wire solder in a gauge that is narrow enough to melt easily with the wire gauge most commonly found on motorcycles, usually 18 gauge for most purposes. I usually buy solder without the rosin core, preferring to use a dab of flux on the bare wires before heating them and applying the solder.

wire splicing pigtail

A pigtail splice is used to send a wire back alongside the wire it is connected to. A good example of when to choose a pigtail or butt splice can be found here.

You should learn how to solder on something other than your wiring harness. For this article, I chose 18-gauge wire in red and blue colors to make it easier to see how they go together. When splicing wires, you’ll usually incorporate one of three kinds of splices: the butt splice, where the two wires are joined to form one, continuous wire; the pigtail splice, where the wires lie next to each other; and the three-way splice, which brings a second wire into the middle of another wire.

wire splicing 3-way

This three-way splice inserts the red wire into the middle of the blue one. This is an example where inferior crimp-on wire taps would typically be used. Don’t succumb to the temptation. While soldering a wire inline is challenging, once taped, this splice is much more secure than any crimped connection.

The first two splices require that about a half-inch of the insulation be removed from both of the wire ends. The ends are twisted together to form a good mechanical bond between the wires. A stand with alligator clips can be homemade or purchased to hold the wires in place while applying heat from the iron.

wire splicing

All three of these splices have been shrink-wrapped. Sometimes, however, tape is the only option in the limited space in which you’re creating the splice.

Before touching the soldering tip to the wires, tin the tip by melting a small amount of solder on it. This helps to spread out the heat when the tip touches the wires. When melting the solder to the wires, try not to touch the iron with the solder. Instead, allow the iron to heat the wire to the point that it melts the solder. Holding the iron below the wires allows the heat to travel upwards while gravity pulls the molten solder down. Capillary action plays an important role in distributing the solder throughout the splice. Touch the iron and solder to a few points on the splice to make sure it is uniformly spread throughout the wire strands. While you want the solder to cover most of the splice, try to avoid leaving big globs of solder on the joint. It looks ugly and will make the splice much larger once it’s covered with tape.

After the splice has cooled, trim any loose wires that could poke through the tape or shrink wrap. Then wrap it with electrical tape or shrink wrap to prevent any accidental grounding against other wires or connectors.

Keep practicing your soldering technique until you are comfortable with it before you attempt it in the most confined spaces of a motorcycle.

  • Starmag

    Hopefully the previous owners of bikes I’ve bought used will read this article and take it to heart, (but I’m not holding my breath). Crimp-ons are “the tools of the devil”. LOL. No doubt.

    • cjmmjc

      if you are reffing to crimp on taps, the you are correct.
      However crimp on lugs (when crimped correctly) are perfectly acceptable and will withstand the vibration of a missile, or weapon launch.
      You would be amazed at the numbers of crimp connections that are in various weapon systems.
      The caveat here is correct tool, correct crimp…. most folks dont have the correct tool, and there foe its impossible to make the correct crimp, (depth, and pressure)

  • bigus brainus

    I still use the good ole Western Union splice. Never lets me down.

    • Evans Brasfield

      They look nice, too.

    • cjmmjc

      kinda hard (id say impossible) to do a WU splice with stranded wire. Any tug on that wire will pull the wires loose

  • JMDonald

    Shrink wrap like the slipper clutch is one of the greatest innovations in motorcycling.

    • Evans Brasfield

      On those odd times that I’ve forgotten to slip the heat shrink on first, I’ve actually unsoldered/resoldered a joint just to avoid taping it.

  • Jon Jones

    Excellent piece!

  • ADB

    “tools of the devil”… Exactly. Great article.

  • Brent S

    Great and well timed article for me. One of my planned winter projects is to tidy up the wiring for the tail tidy I installed. The supplied crimp connectors I haven’t been happy with. 2 quick questions:

    1. Are Posi-Lock connections waterproof? The wiring I want to work on is under the seat but I’d like to stay waterproof anyways.
    2. Where can I go to get some of the different connections? During my quick perusals at Ace, Autozone, motorcycle shops, etc the selections seem very limited. I’d think Radio Shack and I’m not sure if they even exist anymore as I haven’t seen one in many moons.

    • TC

      webBikeWorld has a lot of information about posi locks.

    • Evans Brasfield

      I buy mine from Amazon. If I wait until I have another purchase, I can get free overnight delivery in my neighborhood.

    • Old MOron

      Posi-products claims to have a waterproof version.
      Haven’t tried it, myself.

  • TC

    Great article. The only thing I would add is to keep the tip of your soldering iron clean by sanding it lightly with some 120 grit sandpaper and then ‘tinning’ it by applying a little solder to it. This helps conduct the heat a lot better.

    • cjmmjc

      You should never sand a soldering iron tip.
      You are actually sanding off the coating on the tip
      You use a dampened sponge, yes i said damp sponge, then wipe the tip til clean, then immediately tin it, then turn the iron off.
      The act of wiping it with a damp sponge is called thermal shocking

      I was (got laid of a while ago) am Mil-spec, and Weapon Spec (military) hand solderer and trust me sanding a tip is the quickest way to lose a tip.

      • Evans Brasfield

        Thank you.

      • TC

        I stand corrected, thanks.

  • Ferris Argyle

    Super timely article, thanks. One tip: use marine shrink wrap for a water-tight connection.

    • Doug S

      You can make your own. Squirt hot glue from your glue gun into a cup of water to make long strings of hot glue. Cut a piece the same length as the shrink wrap you’re using, and put it inside the shrink wrap along with the wires just before you shrink it. The glue will melt while the tube is shrinking, encapsulate everything, and you’ll have a more mechanically sound, and completely waterproof connection. Far cheaper than those pre-fab’ed ones.

      • cjmmjc

        Is freaking BRILLIANT
        Im going to try that RIGHT NOW

  • Doug S

    If you’re capable of doing a decent soldering job, it’s not necessary to make the connection mechanically sound first. They teach it to beginners, in the hopes that if the soldering job is subpar it still won’t fail, but it’s a band-aid at best. Soldering the wires side-by-side is perfectly acceptable, provided the soldering job is done properly, and far easier to disassemble in the future if you need to.

    • cjmmjc

      Yes and NO. (mostly no)
      A mechanical connection even if its just a 90 degree hook is mandatory in WS, and mil spec applications.
      The reason is vibration.

      Yes a laid-next-to solder connection is good for 95% of the applications out there, and excellent for everyday folks, however it is possible to and can vibrate and crack even from a motorcycle.

      A joint will have to be perfect to hold w/o some kind of mechanical connection, and most novices are not trained to do this, and internally (where it counts) the joint will not be good.

      • Doug Shepherd

        As I said twice, “If you’re capable of doing a decent soldering job…”.

        Vibration will eventually cause even annealed copper to break; that’s why a proper connection must be strain relieved. Solder is no more prone to breakage than the copper in the wire is. I’m not making this stuff up; I’ve been an Electronics Engineer since 1984, I’ve been to solder school at two different Department of Defense companies, and this is the information they give you there.

        A properly done soldered connection (reasonably clean copper, adequate flux, enough heat) will flow out to cover all the copper, and will be shiny on the outside, not dull in color. If the joint appears like that, it will NOT be suspect internally. Again, IF YOU CAN MAKE A JOINT LIKE THAT, there’s no need for twisting the wires together. If you can’t, you shouldn’t be soldering. Twisting the wires is no substitute for a good solder joint. Use Posi-locks instead.

        • cjmmjc

          WS and Mil spec, mandate a mechanical connection. for just the reasons that I mentioned.

          The minimum, mechanical connection on 2 or more wires to be connected is 1/4 wrap (total spec is 90 deg. to 270 deg. wrap with no copper visible on the cut ends of the wire) radius on a hook connection, and a twist wire connection is not even allowed.

          As for the shiny issue, most Novice, and most commercial solderers do not even recognize a cloudy joint (from either cold solder OR movement of the joint before cooling) as being a faulty joint.

          As far as training goes, I can throw the same set of credentials at you from the exact same sources (does China Lake ring a bell),but the bottom line is you do what you think is best. I will err on the side of caution and a safe solder joint, on my bike.

          You do what you think is best.

  • blinebob

    Excellent article. I know it seems archaic compared to shrink wrap, but I thought I’d add a few words about taping. After all, it may be the only method available during an emergency. The typical 3/4 inch wide roll of electrical tape is too wide for a small gauge wiring job. To cover a joint, the 3/4 inch tape should be cut to 1 1/2 to 2 inch long pieces and then cut in half lengthwise. Use one of the narrow pieces to wrap the joint in one direction, then use another to wrap in the opposite direction. This way there is a double layer and if the top piece starts to unwrap, it will have to unwrap entirely before the bottom piece can start to unwrap.

  • w2e2b

    Why are alligator clips being used to hold the wire and appear to be puncturing the wire insulation?

    • Evans Brasfield

      Good question. The alligator clips are on my soldering stand and are used to hold wires in place while soldering. Normally, I only use then for really delicate joints, but in this case, I used them to hold the wires in place to make it easier to photograph with my macro lens. While they certainly are denting the insulation, they are nowhere near strong enough to actually puncture it. FWIW, most of my soldering takes place on the bike with a piece of cardboard between the wires I’m soldering and the rest of the harness. You can see a photo of it here:

  • Tinwoods

    Articles like this (unglamorous, but ever so useful) are why I continue to follow this site.