How to do a Basic Wire Splice

  1. krazykuda
    Hi everyone! I'm here to show you how I splice electrical wires. One of my old bosses was an electrical engineer and he gave me some advice on how to properly splice electrical wires.

    I've seen many attempts at splicing wires with my cars over the years, and I've seen some real hack jobs. I will walk you through how to splice two wires together for long term service and dependability. This will include soldering, as it is more permanent and will give you many miles of trouble free service when done right.

    Ok, the first thing that you have to do is to strip the ends off of the wire. I like to strip about 1" or a little more for my splices, and you will see why in a little bit in the next section.


    I like my "auto stripper", but you can use the basic wire strippers if that's what you have:

    Wire Splice 2-1.jpg





    Strip the insulation off of the wire:

    Wire Splice 2-2.jpg





    After you strip the insulation off, it will be "frayed" and looks like this:

    Wire Splice 2-3.jpg





    Now you twist the strands of the wire together and they should look like this:

    Wire Splice 2-4.jpg





    Now we move on to the next section on how to connect them....

    Now I will show you how my boss explained the proper way to splice.


    First thing you do before you splice is to cut some shrink wrap (also called heat shrink tubing) and slide it down the wire away from your splice so the heat doesn't shrink it while you are soldering. Get it away from the heat until you are ready to shrink it on your splice. Make sure that you cut the shrink wrap so it covers all of the bare wire and a little of the insulation on each side of the splice.


    Wire Splice 3-1.jpg




    Now, here I am going to show you the "not so good" way of splicing, that I don't recommend. This is where you "hook" them together like this:


    Wire Splice 3-2.jpg





    Here it is twisted together like this:


    Wire Splice 3-3.jpg





    Notice the red part showing how you only have "transfer contact" at the points where the two wires meet, and that's it:


    Wire Splice 3-4.jpg





    Here is the way that my boss showed me how to do a splice. You put the two wire ends together side by side and twist them together along the length of the stripped wires:


    Wire Splice 3-5.jpg





    Here is how you twist them together so they contact lengthwise along the whole length of the stripped wire:


    Wire Splice 3-6.jpg





    Now here is the red line showing how you get more contact along the length of the splice, instead of just point contact as shown above. This way gives you more surface area for your splice and for the current to flow:


    Wire Splice 3-7.jpg


    Now you need to put flux on the wires for the soldering. I like the paste flux as shown, you may also use the liquid, whichever you prefer to use.


    Here is the paste type flux and a flux brush:


    Wire Splice 4-1.jpg





    Now put some flux along all of the exposed/stripped wire:


    Wire Splice 4-2.jpg





    When done, it should look like this:


    Wire Splice 4-3.jpg


    First you need to heat up the soldering iron and get it nice and hot. I like to use a Weller 40 amp soldering iron available at most home improvement/hardware stores. If you are soldering a bunch wires together, you may want to get a higher wattage iron. For this example, I will just splice just two wires together to keep it simple.


    One thing that you will need is a wet sponge. Get an old sponge and cut a bit of it off and get it well soaked in water, but not so much that it drips. Just enough so it doesn't drip.


    Now heat up the iron, and the tip may look cruddy/crappy when it gets fully heated like this:


    Wire Splice 5-1.jpg





    Now you need to clean the tip. To do this, just swipe it along the wet sponge until it looks clean and shiny like this. Don't worry, the sponge will not burn or catch fire when it is soaked with water:


    Wire Splice 5-2.jpg





    Here's what the clean tip should look like:


    Wire Splice 5-3.jpg





    Now you need to "tin" the tip. This is where you melt a bit of solder on the tip of the iron. Be sure to do both sides.


    Wire Splice 5-4.jpg





    Here is a nice clean and tinned tip.


    Wire Splice 5-5.jpg





    Now you are ready to move on to soldering....

    Now we are ready to solder the wires together. I like to hold the soldering iron under the wire to heat up the wire first. You can hear the flux "boiling" while you do this. Then after the wires get good and hot, touch the solder to the wire (not the iron) and let it flow along the whole length of the splice. This will get the best bonding for the solder to the wires.


    Here I am holding the soldering iron under the wires to heat them up:


    Wire Splice 6-1.jpg





    Once the wires are hot and the flux has melted, touch the solder to the wires like this until the solder is completely covering all of the wires:


    Wire Splice 6-2.jpg





    Here is what it should look like when you are finished:


    Wire Splice 6-3.jpg


    Now you need to insulate the solder joint so it doesn't short out. Slide the heat shrink tube over the joint after it has time to cool. Make sure that it covers the whole length of the splice and overlaps the insulation on each side of the joint. You can use more than one layer of heat shrink if you wish. The better it's insulated, the less chance for it to rub through from vibration while you drive.

    I like to use a lighter to shrink the tubing, you can also use a heat gun.


    Wire Splice 7-1.jpg





    Go back and forth along the length of the heat shrink tubing until it is nice and snug.


    Wire Splice 7-2.jpg





    Here's what it should look like when finished.


    Wire Splice 7-3.jpg


    Even with heat shrink tubing, I still like to cover it with electrical tape for extra piece of mind. I like to cover it with at least 3 layers or more of tape.

    Here's me starting to tape the wire. Make sure that you completely cover all of the shrink wrap and a little extra on each end.


    Wire Splice 8-1.jpg





    Here it is with three or four layers of tape over the heat shrink. This puppy should be well insulated and not ground out by now.


    Wire Splice 8-2.jpg





    Here is a bundle of wires that I have spliced on my son's car. After you get all of the wires spliced, then I like to wrap them up like the factory. I use a few pieces of tape along the wires to keep them together while I run tape along the full length of the wires.


    Wire Splice 8-3.jpg




    Here is the bundle all taped up:


    Wire Splice 8-4.jpg





    In case you are curious about what we are working on, it's my oldest son's 72 Challenger Ralley. It's an original triple black car - black paint, black vinyl top, and black interior, 318 car with R/T hood, console, buckets, and ralley dash. The engine is the original 318, freshly rebuilt and we put 360 heads with 2.02" intake valves. My brother bought it from someone that we knew back in high school that was the second owner. He drove it a while, and then sold it to me. Then I drove it for a while, then sold it back to my brother. He has now handed it down to my son. It has just under 100 k miles on it.


    Wire Splice 8-5.jpg





    Now you know how to properly splice electrical wiring. Good luck with your projects. I hope that this will help you if you need to splice any wires.

    Share This Article

      MrJLR, Del and Ters like this.
    1. This site uses cookies to help personalize content, tailor your experience and to keep you logged in if you register.
      By continuing to use this site, you are consenting to our use of cookies.