Technical How to splice wires

[plym49]

There have been a lot of super technical how-to threads posted, and many of them have presented very sophisticated tips and techniques. This one is more modest, but it covers something that all of us do a lot of, and that is splicing wires.

There are many ways to splice wires. Some work well, and some do not. I am going to describe a way that works electrically (does not impede current flow), mechanically (has strength and fatigue resistance) and appearance-wise (for obvious reasons).

First off, I NEVER use crimp-on butt connectors. They are nothing but a shortcut. It's like using hardware store angle brackets and sheet metal screws to fasten your chassis together instead of welding. I realize that crimp-on connectors are accepted and that there is a right way and a wrong way to use them. Crimp-ons were designed for speedy assembly by a less-skilled installer. For that, you get trade-offs like reduced long-term durability.

I will describe an easy method that creates dependable splices that will not leave you stranded some rainy evening, and that only takes a minute or two longer than Slim Shadying your splice with a crimp-on connector.

You will need some tools. We all have tons of tools. These few are the ones I depend upon for most of my wiring.

Obvioulsy, you need a soldering iron. With the dozen or so I have accumulated over the years, there are two I depend upon the most for wiring.

The first is my almost 40 year old Weller. This fugly beast has been used and abused. Half of the case is gone and it is held together with duct tape. But it is a kick-ass unit and it produces enough heat on 'high' to sweat 3/8" copper fittings. Even though I have newer, prettier Weller soldering guns, this betty is my go-to:



My other favorite is a Blue Point unit from the Snap-On guy. It is butane fired, so you can use it anywhere. It heats instantly and the gas valve does not leak when you put it away. It has three chisel tips, three pointed tips and a chimney. I mostly use the middle chisel tip for automotive wiring. The chimney is used to set your shrink wrap.



Next, you need a few hand tools. Again, almost anything goes. Nine times out of ten, I reach for one of these:



Finally, we have what is almost the most important soldering aid you can have. It is home made from stiff wire and a couple of alligator clips. You need to use a stiff wire so that the unit has some spring - we will see why later. I used brazing rod on this one; any stiff wire that springs back will do. This is a really simple, primitive man tool, but as we will see it is also the one that separates the men from the boys:



OK, that's enough to get us started. The next post will get into the actual splice.

[plym49]

On to the splice:

The first thing to do is to remember to slide on the shrink wrap before you complete your splice. There are few things more frustrating than having to cut apart a perfect splice because you forgot the shrink wrap.

Use quality shrink wrap, and buy it in bulk. When you buy it in those little blister packs you are paying thru the nose. This stuff is cheap - order a few sizes so that you have the right ones on hand. Shrink wrap shrinks something like 80%. If you start with too wide a piece, it won't shrink down enough. If you use too narrow a piece, it might split when you heat it.

Also, whenever you use shrink wrap, make sure that you slide it far enough away so that the heat from soldering does not prematurely shrink it. The only thing more frustrating than forgetting to slide the shrink wrap on in the first place is having to cut the splice apart because your shrink wrap shrunk while you were soldering.

OK, so you slide your shrink wrap on one of the wires. Then, strip the wires. You do not need to strip too much. Maybe 1/4" to 3/8" for smaller gauges. Strip both wires the same amount.



After you strip the wire, grab the copper between your thumbnail and your index finger. Drag your nail across the strands so that you untwist them and fan them out. You want the strands straight and slightly fanning out.



Do this for both wires. Again, the strands must be flat and straight and slightly fanned out.



Now, clip your special tool to one of the wires. Position this wire so that the flat, fanned out strands are oriented vertically.



Clip the tool to the other wire. Arrange the wires so that they overlap tip-to-insulation. Also, position the second wire so that the flat, twisted strands are oriented horizontally. At this point the wires are alongside each other.



Now, spring it open a bit so that you can interlock the two wires. The spring tension will keep them in position. You want to interlock the strands of the two wires as neatly as you can.



Use your fingers to squeeze the wires together while twisting the splice. Two fingers twist one way, and the other two fingers twist the other way. You do not want to twist more than about a half turn overall. You are simply getting the strands in good contact with each other. The slight twist and the tool keep everything together. If it falls apart, you messed up, so take it apart and try again. If you try to twist too much, it will fall apart.

When done, it will look like this:



Now, solder. Don't overheat the joint as this will Slim Shady the insulation. Also, don't use too much solder - it only takes a small amount. When all of the strands are covered with solder with a shiny molten appearance, you are done soldering:



Let the joint cool so that the shrink wrap does not shrink from the latent heat on the joint. The only thing more frustrating that forgetting the shrink wrap, or having the shrink wrap too close when you solder, is having the shrink wrap shrink while you try to slip slide it into place.

If you are a super star, at this point you spritz the splice with electronic flux cleaner. Flux is slightly acidic, and can cause corrosion over the long term if the splice is exposed to moisture. This is another reason to not use too much solder. You should use a good quality, rosin core electronic solder. Don't use acid core flux on electronic connections.



The shrink wrap should be three to four times the length of the splice.

There are many ways to shrink the shrink wrap. If you are hard core, you use your lighter. A little less hard core, maybe a small butane torch. Open flames work quickly but you better be good, because it is really easy to charr the shrink wrap or the wire. The only thing more frustrating.......

Heat guns work real well. They still can put out enough heat to char the shrink wrap. Also, once the heat wrap stops shrinking, stop heating it. You can't get it to shrink any more and if you try you will either burn it or split it. Use the right size to begin with.

Here, I am using the chimney attachment on my butane soldering iron to direct hot air onto the shrink wrap. You can see me chasing the shrink wrap along.

You will have to heat both sides of the wire. Heating shrink wrap is line-of-sight. Do one side, end to end, then rotate the wire 180 degrees and do the other side.



Done! It should look like this:



Even though this is a straightforward operation requiring simple tools, it does take some practice. Splice some scraps to get the feel of it. One of the nice things about this technique is that the spliced wire is not much larger than the original wires, making it easy to make a loom, or to run the wires inside a motorcycle frame or whatever.

Good luck!

[Kustom7777]

good tech,,thanks
i like neat wiring,,this is very useful

[M_S]

Originally Posted by plym49

First off, I NEVER use crimp-on butt connectors. They are nothing but a shortcut.

Then why does the FAA only allow crimped electrical joints?

[HotRod_Joe]

Great tip! One thing you didn't mention (or atleast I didn't see) is that the idea is to heat the wire with the soldering gun, and use the hot wire to melt the solder. Also, if you're using a heat gun to shrink your shrink wrap, they make a deflector that's a half round so it'll shrink the wrap evenly all around. Another thing, when I solder wire I also like to wrap the shrink wrap with electrical tape for an extra bit of protection.

Again, great tip!

[choppintops]

Originally Posted by M_S

Then why does the FAA only allow crimped electrical joints?

Because they allow anything to fly

[waltmcq]

At a trade show I saw a solder,crimp, shrink wrap fitting all in one

[electrodude]

There are some sweet connectors out there now that you heat and they melt the solder internally, the shrink wrap already on them. There is also some kind of sealant under the wrap that basically glues the whole mess together for a perfect impenetrable seal.

Pretty expensive but worth the cost if the wire is going to be covered (hopefully) forever. We use the crap out of these for permanent repairs on equipment when we're on a breakdown and there's no time to set up for a proper solder.

I also just cannot stomache crimp connectors. IF you use a good crimper and IF you seal it well you might have a good connection. Relying on that thin strip of metal over the long term is not a good idea though, in my humble opinion.

Nice thread by the way

[plym49]

Originally Posted by M_S

Then why does the FAA only allow crimped electrical joints?

Beats me. Ask the FAA.

I am quite sure that airframe mechanics don't use the Harry Homeowner grade materials that show up in the automotive trade. Whatever they do must produce perfect connections. Aircraft use 400 cycle AC, are concerned about problems above and beyond those we face, and so on: the entire landscape is different.

Many automotive connections are crimped by the factory, and work well forever. The tools, techniques and materials they use do not correspond to every day work.

IMHO the majority of 'aftermarket' crimped connections - you know the ones I mean - are failures waiting to happen.

[kustombypook]

I have always been told to NEVER solder wires in cars, planes, boats or any kind of vehicle that is prone to vibration. Vibrations can cause a soldered joint to crack. The same reason solid wire is not used in cars.

[plym49]

Originally Posted by HotRod_Joe

Great tip! One thing you didn't mention (or atleast I didn't see) is that the idea is to heat the wire with the soldering gun, and use the hot wire to melt the solder. Also, if you're using a heat gun to shrink your shrink wrap, they make a deflector that's a half round so it'll shrink the wrap evenly all around. Another thing, when I solder wire I also like to wrap the shrink wrap with electrical tape for an extra bit of protection.

Again, great tip!

Yes, I did not mention that. I lay the wire on top of the iron, and then I touch the solder to the tip of the iron. Just a tiny drop. The molten drop of solder tranmits the heat to the wire faster. Then, when you see that drop of solder wick into the wire, you touch the solder to the wire and the rest wicks in.

That's a good idea about the heat gun deflector.

You can certainly wrap the entire thing with tape. I suggest using self-vulcanizing tape. It never unravels or gets gunky because of exposure to gasoline.

[plym49]

Originally Posted by waltmcq

At a trade show I saw a solder,crimp, shrink wrap fitting all in one

I've heard of them, too. Never used one, though.

If you are running wires inside of a frame or handlebars, you don't need the extra width of a connector, for sure.

[plym49]

Originally Posted by kustombypook

I have always been told to NEVER solder wires in cars, planes, boats or any kind of vehicle that is prone to vibration. Vibrations can cause a soldered joint to crack. The same reason solid wire is not used in cars.

That kind of generality does not make sense.

There are circumstances where that can be an issue, and whether or not it is soldered. However....

A 'stiff' quarter inch splice is not going to cause any problem, and this is not the same as running solid wire end-to-end.

[M_S]

Originally Posted by plym49

Beats me. Ask the FAA.

I already know the answer, the question was rhetorical.

A solderless joint can be every bit as good as a soldered joint and vice versa. A bad solder joint is easier to make than a bad crimp, even for those proficient with solder joints. A good crimp made will produce a joint with less resistance than the wire it replaces.

To liken them to holding a chassis together with sheet metal screws is unfair.

There is nothing wrong with a soldered joint either, but it's tougher to do correctly.

[gassman57]

Originally Posted by waltmcq

At a trade show I saw a solder,crimp, shrink wrap fitting all in one

The Belden Wire Co. makes them; a.k.a. waterproof connectors. We would use them in all the marine applications in the shop. Wou'll find them at your neighborhood NAPA.

[choppintops]

Originally Posted by plym49

That kind of generality does not make sense.

.

Much like the ones you made on crimp connectors.

[29nash]

Originally Posted by M_S

Then why does the FAA only allow crimped electrical joints?

Soldered joints are rigid, and fracture when in a vibrating environment which all airplanes do. They vibrate.

Crimped joints work good and last a long time, maybe a lifetime, maybe into eternity, who knows? It's not the joint so much as the proper way its done. Where crimp fails is when the wire is improperly supported and the pulling on the wire itself puts a load on the joint. In a vibrating situation, like a motorcycle, a soldered joint is just as likely to break as a crimp. Solder precipitates down the strands in the wire and makes it rigid. Vibration tends to fracture it. Stress, (tension), combined with movement, (vibration), is the enemy of any splice.

[plym49]

Originally Posted by M_S

I already know the answer, the question was rhetorical.

A solderless joint can be every bit as good as a soldered joint and vice versa. A bad solder joint is easier to make than a bad crimp, even for those proficient with solder joints. A good crimp made will produce a joint with less resistance than the wire it replaces.

To liken them to holding a chassis together with sheet metal screws is unfair.

There is nothing wrong with a soldered joint either, but it's tougher to do correctly.

I don't disagree that some crimped connections can be OK. I myself have high-end crimpers for specialty items, like fuel injector terminals.

The garden variety crimp connectors most people use provide little if any corrosion protection, and no long-term mechanical integrity. You can slip slide a connection together in moments, but that connection right there is the one that will fail on you one day.

It's easier to make a bad weld than a good weld. So should we all stick to bolts?

That might have also been unfair. Hey, if crimped connections float your boat, go for them. This tech was about a technique for soldered splices, and IMHO this is often a better alternative.

[plym49]

Originally Posted by 29nash

I know this, as an Aircraft technician/inspector/mechanic examiner. Soldered joints are rigid, and fracture when in a vibrating environment which all airplanes do. They vibrate. Crimped joints work good and last a long time, maybe a lifetime, maybe into eternity, who knows? It's not the joint so much as the proper way its done.

Aircraft are their own special thing, because the stakes are high.

Splices are usually somewhere in the middle of a loom, so vibration-induced fatigue is not an issue because everything is able to move. If you hold everything else fixed and only the connection can flex, a soldered joint might fail first but even a crimped joint will eventually fail as the copper wire work hardens where it goes into the crimp

Motorcycles vibrate a lot (ever try to keep parts on a Harley? Thank God for Loctite.) and the soldered splice as I presented holds up very well in those environments.

[Hakoval Traedz]

Good post. I hate the snake-swallowed-a-mouse look of a crimp-connector splice in a wiring harness. I worked for Ma Bell years ago, and soldered hundreds of wire terminations daily for several years (granted--completely different world from car wiring) but one point taught in telco training was that solder is meant to provide a mechanical connection, not an electrical one. If the metal/metal contact before soldering is not good, even a soldered connection can have excessive resistance. I need to practice the interwoven strand technique--usually rely on a western union twisted splice myself.