Electrical Wire soldering For Beginners
by Randy Glass
DISCLAIMER- First, soldering can be dangerous. This lesson is not meant to be everything you need to know. Your safety is up to you, and you take full responsibility for any damage or injury caused by these instructions, whether as an act of omission or commission on your part or mine. Be aware that an improperly soldered wire can lead to fire, loss of vehicles, injury, and even death. By reading and/or using these instructions you take full responsibility and release me from all liability. Second, I took these photos as I did the work, pressing the remote control for my camera with one finger as I held the soldering pencil in one hand and the solder in the other.
I apologize for any images that might be out of focus or poorly composed.
If Yogi Berra ever wrote a book on motorcycles he would probably say, "We seem to spend around forty percent of our time taking things apart, and the other seventy-five percent of the time putting them back together." Some things are easy to put together. We use specialized fasteners like nuts, bolts and screws to hold things together that, some day, we might want to take apart again. But there are some things that, once put together, we would like to know that, to some degree, our fastening system is permanent. One of those places is in electrical wiring.
When a wire breaks or needs to be fastened to a connector or another wire in
such a way as to be dependable, then the very best way is to solder.
soldering is a method to attach one metal part to another. It is part of a family that uses molten metal to do this job. At the top of the ladder is welding. This is a very high temperature method that actually melts the parts a bit where they are attached, along with some other metal, usually in the form of welding rods. Next is brazing. This melts some hard metal, usually brass, into the gap between two pieces of metal. Normally, the surface of the material being joined is not melted in this process, but it gets very, very hot. Finally there is soldering.
soldering flows some molten metal between metal parts at relatively low
For our purposes I am going to
speak of the type of soldering that attaches two wires together or one wire to a
connector- the sort of soldering that any backyard mechanic might need to do
when working on any electrical component or the wires that connect them together
in almost any type of vehicle.
Although there are methods that can be used to make these connections without soldering, they are usually inferior. soldering does a lot of things:
1) It Is Strong- You are connecting two metal parts with a liquid metal that becomes solid after it fills the joint and cools.
When properly done it leaves no voids so the joint is very strong and the wire
is well supported.
2) It Slows or Stops Oxidation - Because solder fills the joint it excludes air and moisture so the metal in the joint will not oxidize.
This maximizes electrical flow over time.
3) It Makes An Excellent Electrical Connection-
because the solder is a conductor it gives the wire more area from which it can
flow electrons to whatever it is connected.
4) Non-permanent - Although soldering is very strong,
it can be removed and the joint taken apart in the future if necessary.
5) Connectors do Not Need to be Crimped - Those little metal connectors that are designed to be crimped have a terrible habit of coming loose as well as breaking the little copper wires in the conductor making a weak joint as well as one that does not conduct as well as it should.
They easily let air and moisture in which causes corrosion and that leads to
poor and broken connections.
It doesn't take much to set yourself up as a soldering wizard. Here is a list (numbers refer to image to the left):
*1) soldering Pencil - Something around 25 to 40 watts would probably be fine for most electrical work. You don't need a huge soldering gun to do electrical work. A little smaller is actually better than too big, as we shall see. Get a brand-named pencil so that down the line you will still be able to get replacement tips for it. A chisel tip as seen in the pictures that follow is best for most work but you might also need a pointed tip for more delicate work. Those old soldering guns are nice for making battery cables, but are generally too large for what we are doing. it would be like using a sledge hammer to make a picture frame- it would have to be a REALLY big picture frame!
There are also cordless, rechargeable soldering irons available. They generally run about $35-75 or so. Although these cost substantially more than a corded iron, and the replacement tips are more expensive as well, there is no cord to get in the way when working and as they can be carried along on trips. These generally have a built-in light as well making repairs at night easier.
I normally loosen the lamp so that it does not light, so the battery lasts
longer in use.
There are soldering tools that are actually little, refillable, butane-powered torches with a soldering tip at the end which is heated by the flame. As they are about the size of a fat ball point pen, they are another good way to get a portable soldering tool. These generally are available for less cost than the rechargeable irons mentioned above.
I have used electric irons to solder around a gas tank on an automobile-
something that I would never consider with one of these.
And a soldering Pencil Holder - Most soldering pencils come with a holder or a rest as seen here, but if not, get one.
These metal stands are very handy and will help avoid melted parts and burned
hands and work surfaces.
*2) solder - Resin core solder is what you want. NEVER use acid core solder on electrical components.
The acid will stick around and continue to eat into components and wiring well
after the soldering job is over.
Resin core solder can be had in various quantities, but I buy the one pound roll for around $12-15 which will be a lifetime supply for most folks. I use Kester brand "44" Resin Core solder in the .031 diameter size.
This is about the size of mechanical pencil lead and works quite well for what
you will be doing.
It use to be that a standard part of a soldering kit was a little tub of flux. This paste would be spread on the joint ahead of time to help clean the joint chemically as it was heated by the iron. It was necessary as flux-core solder was unavailable.
If your wires are clean and you are using a quality, resin core solder,
additional flux is not necessary.
*3) An Old kitchen sponge or two
* Tools to work on wires such as a (4) wire
stripper and a (5) wire cutter, and possibly needle nosed pliers and a small
vise (not shown).
* 6) A few bits of insulated wire and an old spade connector or two on which to practice.
Two or three feet of wire will do.
*7) Heat Shrink Tubing - I rarely use electrical tape any more. Heat shrink is really great! I usually buy it in three foot lengths in two or three sizes. This is a sort of memory tubing that, I believe, is made by heating a special tubing and stretching it and allowing it to cool while still stretched. it maintains that size.
When heat is applied once again the tubing will shrink back down to its original
*8) Protection for the work surface like an old piece of 1/4" plywood about 12" square or such.
An old piece of counter-top lamination works also.
* Wicking material (not shown)- You can purchase some special copper wick that is used to unsolder joints.
This is usually not necessary, but handy at times, and inexpensive.
* Eye protection
* A Ventilated workspace
HEAT - A soldering pencil as well as molten solder are both really hot. They will burn you and it will hurt. It can hurt a lot. It can make your skin give off smoke and that smells bad. If left unattended a hot soldering pencil can cause fires, melt carpeting, burn workbenches, and make the cat dance like never before. An unsuspecting person can pick up a hot soldering iron and get a nasty burn (trust me on this one!).
Never leave a soldering tool warming or hot and unattended.
Additionally, a hot soldering iron can almost instantly melt plastic parts and upholstery in a hurry. Use care when soldering as well as when moving the iron to and from the solder joint. If the cord gets caught when moving the iron it can easily cause you to drop the hot tool onto something expensive or painful.
NEVER place a soldering iron on saddles, luggage, body work, painted surfaces,
or on or near any heat-sensitive surface.
LEAD and VAPORS- solder contains a good amount of lead and handling it over a long period of time may have negative health consequences. The vapors caused by soldering can, over time, cause health problems as well. Work in a well ventilated area. I usually work out doors and use a fan to blow the vapors away from me.
The smoke that is given off by the flux in the solder is also not a good thing
MOLTEN METAL - When soldering (and particularly when un-soldering) it is very possible to flick bits of melted solder about. As this stuff is quite hot, even a small drop in the eye can cause permanent damage. Wear eye protection and do not wear your good glasses, or wear them under goggles. The dripped solder can melt plastic parts and permanently damage auto carpeting as well.
Be aware of other folks or critters who may be in the area as well.
ELECTRICITY - You will be soldering on wires that, if shorted out, could cause a blown fuse, damaged electrical components, or melting wires and a fire.
Always disconnect the battery when soldering wires on a vehicle and remove
connectors from heat-sensitive components before soldering on them.
I could spend a lot of time talking about how it all works, but jumping right in is the best way to learn how to solder and I will explain as I go
Begin by creating a safe work area. One free of clutter, with sufficient light, and protected from the soldering iron and melting solder. Set the soldering pencil in its stand and plug it in. be sure that the cord is placed in a way that it will not be accidently
pulled or tripped on, upsetting the soldering pencil.
While that is heating up, prepare your sponge.
Wet it, squeeze out the excess water, then fold it in half and rubber band it
about half-way down.
Pull out about a foot or two of solder from the roll and touch it to the tip of the soldering iron. Always apply the solder to the flat parts of the tip and not to the sides. When the solder melts fairly easily, melt an amount all over the tip.
There will be some smoke from the resin in the solder.
The solder you bought is actually a bit hollow. Inside of the metal there is a channel (or in some cases, channels) that make it sort of like a little garden hose. The channel is filled with a resin. When heated it melts and some of it burns off. The action of the resin when it is heated helps clean the surface to be soldered which helps the solder stick a lot better. Unfortunately, the burned resins can also leave deposits on the soldering pencil, and over time will make it difficult to solder. That's where the sponge comes in.
After you have melted some solder onto the tip (about a quarter inch or so of
the thin stuff) wipe the soldering pencil's tip off on the damp sponge a few
If you examine the tip of the soldering pencil carefully you will see that it is now covered with a thing coat of shiny, silver metal- the solder. You have successfully "tinned" the tip of the pencil. This keeps the metal tip from oxidizing and will assist you in soldering from now on.
Always do this before starting a soldering job and occasionally during a larger
Place the soldering pencil back into its holder and let's prepare the wires.
We are going to solder two wires together, making believe they have broken or
We start by "stripping" some of the plastic insulation away from where we want to connect the wires. The thicker the wire the more insulation we remove. For most common wires on a motorcycle or in a car, removing about 3/8 to ½ inch works fine. You will get a feel for how much in a short period of time.
When stripping wire be very careful not to cut the strands of the conductor.
There are special tools available for stripping wire that can save a lot of time.
These can be as simple as a carefully wielded razor blade to fancy and somewhat
expensive automatic strippers.
Once stripped, twist the
strands together into a neat little bundle.
The exposed wires should look fairly clean and in most cases, shiny, but certainly not green or cruddy.
If corroded, then the wires should be cut back and re-stripped until clean wire
Now cut a length of heat shrink tubing off about an inch long. It should be of a large enough diameter that at least two of the wires you are soldering can easily fit into it at the same time. Slide the length of the tubing over one of the stripped wires- it doesn't matter which here, but in real life we would slide it over the lower wire or the one which slopes most downward away from the joint so it will tend to slide out of the way.
make sure it is at least three or four inches away from the joint.
Now, twist the two wires together into a tight, neat pair. This is important because it helps create a good electrical connection. You also do not want any little wires sticking out. Start by crossing the wires about mid-strip, crossing them at about 45 degrees or so, and twisting in opposite directions. When done, the joint should be fairly strong on its own, holding the two wires together tightly.
The connected pair of wires should be in line as if they are a single wire and
not two joined together.
It's time to solder. Place the roll of solder on your left (if you are right handed) with a good length of solder hanging out of the roll. With the solder in your left hand and the soldering iron in your right hand, check to see that the tip is still tinned and shiny.
If not, repeat the process with a bit of solder melted to the tip, then wipe the
tip off on the sponge.
Melt a little ball of solder
onto the iron....
...and immediately place the soldering iron under the twisted wires (if possible) so that the little ball of solder fills much of the gap between the soldering pencil and the wire. Since heat rises, placing the iron under the joint will heat it faster. The little ball of solder works as a heat conductor and will very rapidly conduct the heat from the soldering pencil's tip into the wires. If the ball of solder does not seem like it is contacting the wire very well, without removing the pencil from the joint, melt just a bit more solder in there by feeding the end of the solder wire into the tip.
This will not only increase the contact area of the solder to the wire but it
will also add a bit of flux that helps the solder adhere to the wire at this
After about two or three seconds, start to feed solder, slowly at first, into the void between the pencil and the wire.
You should soon see the solder is flowing into the twisted wires. WHen that happens, increase the feed rate of the solder into the joint, and you can now also feed a little into the top of the joint. Don't move the iron's placement, jut take the end of the solder wire and touch it to the tip of the joint. Continue to feed solder until the individual wires are almost filled with solder and the entire joint has turned silver.
When that happens, stop feeding the solder in and immediately but gently remove
the soldering iron.
How long do you wait until feeding in solder? One way to test how long to wait is to touch the solder on top of the joint and wait until that area is hot enough to melt the solder. The amount of time it takes varies with the size of the wires to be soldered, the size of the solder, the wattage of the iron, the size of the irons's tip, the ambient air temperature, and other factors.
Experience will teach you how long this takes.
The problem comes from waiting too long and putting too much heat into the joint. When you do that it begins to melt the insulation on the wires around the joint (you can see that beginning to happen above at the end of the insulation of the green wire next to the soldered joint). That is why I like tho flow the solder in from where the iron's tip touches the wire. This is the place that will come up to soldering temperature first, and then the flowing solder will more easily flow solder into the joint as it carries heat with it. The larger the wires, the longer it takes and the more important it becomes to feed in some solder from the top of the joint as well.
Again, experience will teach you when that is necessary.
How much solder is enough? Too much? The correct amount of solder is used when the joint is fairly all silver colored but still shows the "outlines" of the individual strands of wire in the joint. If there is very much in the way of copper colored wire showing then you probably didn't use enough solder or the wires weren't clean and would not accept the solder.
If there are big blobs and drips of hardened solder on the joint then you
probably had either too cool of a joint or used too much solder.
After soldering, let the joint cool for about thirty seconds to a minute or so before handling. If you were successful you should have:
* A pair of wires tightly joined together
* The joint between them is very shiny, looking like polished
* No hardened dribbles or drops of solder hanging off the joint
* No little wires sticking out of the joint.
* A union only slightly larger than each of the wires
If you were NOT successful you might see:
* Large blobs or possibly a long, pointy finger of hardened solder hanging off the joint. Sometimes, after cleaning the iron, these can be removed by simply heating the joint until the solder melts, then removing the iron which will pull away some of the excess solder with it.
This may need to be repeated a few times to remedy the situation.
* Wires that are not soldered together and has movement within it.
Re-heat the joint and add some more solder.
* Melted insulation. This can be so bad that the wires are revealed with the insulation dripping off the wires.
At this point you will probably need to cut the wires and begin again, or
unsolder the joint and add a long piece of heat-shrink tubing to cover the
* Little ends of the copper wires sticking out. These
can sometimes be cut off with a wire cutter and/or pressed down with a pair of
smooth-jaw pliers, possibly needle nose pliers.
Now it is time to cover the joint with the heat shrink tubing.
You DID remember to slide on the heat shrink tubing before beginning, didn't
you? Once the joint is cool enough to touch, slide the tubing so it is centered
over the joint and gently touch the meaty part of the soldering iron's heating
element to the center of the tubing.
Continue this around the center
of the tubing until it tightly grips the wire joint, then work outwards until
the entire piece of tubing has shrunk tightly around the joint.
Attaching An Electrical Connector
Besides connecting two wires together, soldering is the best way top attach some sort of connector to the end of a wire. The connection is strong as well as fairly well sealed against the elements.
It works pretty much the same way as above...
Remember when we "tinned" the tip of the soldering pencil? We did this to apply a film of solder to the tip so it wouldn't oxidize and thus be able to more easily transfer heat.
Now I am going to do the same with a piece of wire.
Here I am applying a good amount of solder ahead of time to this wire because I am planning on soldering it to a fairly heavy connector.
This way, the wire will be "pre-soldered" and easier to attach, and will have
less of a chance of melting the insulation.
When soldering a connector to the end of a piece of wire it is very helpful to use some sort of vise to hold the connector. A small pair of locking pliers or a pair of needle nose pliers with a rubber band around the handles to hold the jaws shut works well. Here I have locked a pair of locking pliers into a small vise to work as a "hands-free" holder.
This not only allows me to use both hands to work but isolates me from the heat
of the soldering process.
Remember that the heavy metal pliers will work as a heat sink, pulling heat away from the soldering joint, so it might take longer to achieve the proper heat level in the joint. That is why I have gripped the connector as far away from the area to be soldered as possible,
Be careful as the pliers may get hot near the tips and you might overheat the wire as well. Be sure to slide the heat shrink tubing over then wire BEFORE beginning to solder! If you leave it off and finish soldering, you will be left with the soldering job in one hand, the heat shrink tubing in the other hand, and a stupid look on your face. We call this, "Heat Shrink Tubing Syndrome."
Additionally, if you apply too much solder, particularly with a small connector, it is very possible to fill the connector with solder and thus make it difficult or impossible for the connector to function properly. There are ways to get the solder out, but they are generally more difficult (or dangerous) than just chucking it and starting over. To keep this from happening:
* Never touch the area of the connector where you don't want solder to flow
* Orient the connector with the part where solder shouldn't flow,
upwards (or Higher than the end where solder will flow).
* Apply solder sparingly and slowly
* Use a lower wattage soldering pencil
* Use a smaller tip on the soldering pencil
I sometimes use two pieces of heat shrink, one over the other, shrunk one at a time, in areas where extra protection is needed. This is particularly useful when soldering a connector to the end of a wire. I first shrink a small diameter piece about an inch long over the wire up to where it joins the connector as shown here.
This acts as a strain relief as well as insulation.
Notice the small amount of flux on the connector ring left over from the soldering process. If you use resin core solder, this stuff is harmless to the electrical device.
It can be brushed off with a small wire brush if you wish.
I then shrink another larger diameter piece about ½ an inch long over the connector to act as an insulating cover. In the case of something like a female spade connector, the entire connector except for the opening can be covered and protected in this way. If the heat shrink interferes with the connection, simply cut the offending part away with a razor blade being careful not to damage anything else including yourself!
In areas where the joint needs to be protected from corrosion, slather the
terminal with petroleum jelly, or the special
grease for this application.
Following these directions you will become a "master solderer" in a short period of time.
It takes some practice to get a feel of how hot for how long with how much
solder it takes to create to make a good solder joint, so get some scrap wire
and practice before attempting to solder on anything important.
If there are any questions or comments, please feel free to E-mail me at