Last updated on May 4th, 2018
Most people wouldn’t believe how controversial this topic still is. Should I crimp or solder this connection? Ask this in any forum and you’ll find opponents willing to passionately debate the topic to death.
On one side you’ll find those who will quickly crimp a connection without giving it a second thought and go on with their day. On the other side you’ll find those more than happy to call the first group “hacks” or lazy. They will insist that a soldered connection is much more reliable and has better performance. But who is right?
The truth of the matter isn’t that simple.
To Crimp or Solder, That is the Question
While it may be painful for some people to hear, the reality is that in the automotive industry this has long ago been settled. The gold standard is to (properly) crimp wires where possible. This is what industry does, and what you should do, too. Whether you’re splicing or attaching a terminal makes no difference. To verify this just take a look under the hood and you’ll find hundreds of crimps, but virtually no soldering. As long as you have the right tools, crimping is the way to go.
Personally, I used to crimp and then solder my connections thinking I was doing myself a favor reliability-wise. Then I had a few electrical problems on some custom systems. They were due to wires breaking due to wire fatigue from normal bending and vibrating, combined with corrosion. Just tugging on the connector you could break off the few strands still holding it together. And this was on a carefully tinned, crimped and soldered connection with a quality wire. Heat and humidity played a huge factor, though. After not insignificant research, it quickly became clear that there are plenty of reasons why you shouldn’t be soldering on vehicles.
Note: The following focuses on wiring or terminal connections for automotive applications – namely cars, motorcycles, electric vehicles, marine, etc. Applications which are subject to vibration, heat, movement, thermal shock or similar challenges. Keep in mind that this does not apply to circuit boards or other cases where the wires are immobilized.
Why is Crimping Superior to Soldering?
Since crimping was first introduced in the 1940s, it’s made itself a staple in any assembly plant. It’s quick and easy to do, even more so than soldering. It almost feels too easy, which is why some people feel like it’s the lazy way to do things. But surely just clamping down a terminal on a wire can’t provide a more secure connection than a terminal lovingly hand-soldered by a careful DIYer?
The main issue is wire fatigue. With crimped connections, the wire is free to move at its leisure. Copper is fairly flexible when finely stranded, which is great in a vibration-happy environment like next to a running engine. The crimp is designed to hold the wire securely, while also allowing it to move.
When you solder the wire (either before, after or instead of crimping), unless carefully done, the wire stiffens. It might happen due to excessive heat but it mainly happens thanks to solder getting under the insulation by capillary action. If you apply heat too long (using too small a solder iron), it’s pretty much unavoidable. For soldering newbies it’s even worse, as they tend to apply too much solder to begin with.
When solder gets past the insulation, the wire loses flexibility. Just try bending a soldered wire splice to see it for yourself. If you install it on a vehicle, every vibration is like bending the wire a little bit. Eventually the cables shear off little by little until there is nothing more than a few strands holding it together. As the cable’s effective diameter reduces, the intermittent failure issues start popping up. Finally, the solder-reinforced wire fails.
This is even worse on motorcycles, thanks to their reduced weight and high vibrations. Furthermore, its wiring is generally exposed to high heat and to the elements (read water) which compound the issue with accelerated corrosion.
At a first glance, it might seem like soldering provides a lower resistance than crimping. Surprisingly, reality differs. A properly crimped connection actually creates a metal-metal colloidal bond at the surface between the wire and the terminal. This makes it effectively gas tight, stopping oxidation inside the joint. The copper-on-copper connection is generally superior to solder considering that most solders have more resistance than copper.
In practice, the difference in resistance between either methods (properly done) is beyond the accuracy range of average multimeters. Hence, the difference is negligible, especially when working on 12v circuits. By that my point is that soldering will not provide “better conductivity”. Once you see the cross-section of a properly crimped cable, where the individual strands can hardly be distinguished, it’s easy to understand why.
There are other situations where soldered connections may fare even worse. In a hot engine bay, solder recrystallization can happen over time. This can both increase the joint resistance and lead to cracking. Because of this, solder should never be used to mechanically fixate a wire. And that’s one reason why the American Boat & Yacht Council Standards excludes solder as the sole means of electrical connection for wire terminations. The same situation applies to many military and aeronautic standards.
Finally, if that isn’t enough to be convincing, consider that tin (the main component of most solder) has about 5 times the resistance of copper. As such, when used in high current applications (think a battery lead), that resistance can lead to heat. Apply enough current and the heat can quickly spiral out of control. The resistance creates heat at the joint, which melts the solder, which increases the resistance until it fails altogether. As unlikely as that sounds, it’s a perfectly valid concern and does happen.
Give Crimping a Chance
I’m sure that many of you would love to call BS and tell me how they’ve used X method for years without ever having a problem. I’d probably even agree with them that what they did was perfect, in their situation. Almost any soldered joint will last forever if done right and strain relieved – that’s the key. Nonetheless, none of that takes away that on a vehicle, a decent crimped connection will reliably be less problematic than a decent soldered one. You may disagree, but this is a well-settled fact.
That doesn’t mean that soldering doesn’t have its place. For light-duty, low current tasks, or where crimping isn’t viable, soldering still is a valuable option. A perfect example is any circuit board. It will simply require extra care and attention to do right. But for everything else crimping should be the default choice.
How Do I Properly Crimp a Connection?
So you’ve made it this far and, though skeptical, you’re willing to give it a try. Problem is, you’ve never given crimping a second thought and always used the chintzy tool that came with your $5 kit. No instructions came with it (of course), so you learned as you went. But, what’s the right way to do it?
Tools and Materials
Any project starts with the proper tools and materials. In this case there are several involved.
The first would be to select the proper wire. Don’t underestimate its importance or complexity. There are a daunting amount of wire qualities and specifications for different applications. That includes both the sheathing (PVC, GXL, SXL, TXL…) and the conductor itself (copper, copped-clad, etc…). Click here for a quick overview. Choose the right wire gauge depending on its length and current draw based on a amps-gauge chart.
Oh, and by the way. Don’t judge a wire’s gauge by its outside diameter. Many vendors these days use thick insulation with a thin wire underneath to trick buyers. This is especially problematic when using generic speaker wire for electrical projects.
Crimp Connectors or Terminals
Choose the right Crimp Connector. Not all crimp connectors have the same design, quality, material or strength. When possible choose a high quality kit. For insulated terminals, I prefer nylon (the translucent ones) over PVC insulation. Seamless or brazed barrels are also preferable, as crimping is more consistent.
Depending on the job you may prefer an insulated barrel, or an uninsulated barrel. For ground wires I tend to use uninsulated. Many DIYers prefer to use uninsulated and add their own heatshrink later. If you will be pushing the connector to its current limits, uninsulated is also best as it is easier to get a reliable crimp. But in practice, the decision will depend on the application.
This would be an example of a decent affordable crimp connector kit. There are better, just keep in mind that the high quality kits get expensive, fast. Whatever you decide, make sure to choose the right size for your wires. Thankfully most crimp connectors are color coded as follows:
- Red: 22-16 AWG
- Blue: 16-14 AWG
- Yellow: 14-12 AWG
Next comes a quality Wire Stripper. There are many different types and formats depending on the job, so it isn’t really possible to pick out a single style.
On the basic side you have something like the Irwin Wire Stripper/Cutter. It will do the job just fine for cheap as long as you know how to use it correctly. Though personally what I tend to use most these days is the Capri Tools Automatic Wire Stripper/Cutter. I find it easier to use on wires still connected to the vehicle, thanks to its pistol-grip design. Also, its V-cutter helps strip the wire without nicking the conductors or ripping the sheath.
And finally a good Ratcheting Crimper. This is probably the most important component, and I wouldn’t recommend skimping. Personally, I use the Astro Quick-Change Ratcheting Crimping Tool. It’s excellent thanks to its quality and multiple jaws. But if you’re on a budget you can get an inexpensive one like this IWISS Crimping Tool. The fact that it is ratcheting and will automatically release when the correct pressure is reached greatly aids in not over-crimping.
The most important thing to make sure of is to choose one that has the correct jaws/anvils for the job. If you know you will only be crimping one style of terminal, a single fixed jaw is fine. If you are unsure or would rather future proof, a model with multiple interchangeable jaws is definitely preferable. Even better if they can be swapped tool-free.
While it may be tempting to use a Stripper/Crimper/Cutter Combination tool, I’d recommend avoiding them for crimping. Some are decent, some are junk. Personally, I’d definitely go with the ratcheting style considering that nowadays they don’t cost that much. Using the right crimping tool with a quality jaw is going to have the biggest impact on producing a good crimp.
Crimp ‘er Up
Crimping isn’t particularly difficult, though there is technique involved. While objective, well-defined technical specs on what is and isn’t a well crimped connector exist, the main points to keep in mind are as follows:
- The stripped wires or remaining insulation should be undamaged – That means avoiding cut or nicked strands. The insulation shouldn’t be tapered or torn where the insulation was removed. Make sure the conductors at the end aren’t cut at an angle, either. All of these are reasons to use a good stripping tool.
- There are two types of crimping terminals:
- Closed Barrel Terminals – Here, the portion of the terminal that is crimped forms a closed circle. It is the style typically seen with the opaque plastic insulation included with most budget kits. On this model the crimp barrel should only clamp on the exposed conductors (as opposed to the insulation).
- Open Barrel Terminals – You will typically find this type installed in modular quick-connect plugs. They have two sets of open “wings”. One crimps over the conductor, and one set crimps on the insulation. Though a bit harder to consistently crimp, they are preferable for automotive applications as they provide better strain relief. Make sure that the conductor crimp is only crimping the conductor, and the insulation crimp is only crimping the insulation. When crimping this type of terminal, using the right tool with the right jaws in crucial. Don’t even look at those needle-nose pliers.
- The wire strands should slightly protrude from the front of the wire barrel, but not excessively – This should be the case regardless of the terminal type.
- Correctly place the wire in the terminal before crimping – Center the wire in the terminal and inspect its position prior to crimping. If it is a closed barrel design, you want the seam to be opposite from the detent on the crimping tool. That is called “saddling the seam”. It helps avoid issues with the crimp separating at the seam.
- Be careful with over-crimping – Over-crimping a connection work hardens it making it brittle and prone to failure. One benefit of ratcheting crimpers is that they will automatically release when they achieve the proper crimping pressure. Of course, don’t under-crimp either since that is just as bad.
- Where possible, protect the crimp from corrosion – If you are really concerned with corrosion and moisture wicking, you can use some dielectric grease, conformal coating or liquid electrical tape.
- Add strain relief when possible – Though crimped terminals cope better with repeated bending than soldered connections, don’t abuse it. If the wire will be unsupported and under any strain, at a minimum add some heatshrink as strain relief. Even better if it is the double-walled adhesive variety. That style is sturdier and provides some protection from water ingress thanks to the glue.
- Inspect each crimp – Give each crimp a light tug as a quick test. You’d much prefer it fail now that you’re working on it, rather than a month down the road. Also, give it a few bends to see if that loosens the wire. If done properly, it should feel secure and trust-inspiring.
Keep all of this in mind and your connections are likely to outlive the vehicle, as most OEM crimps do. As long as you do it right, there isn’t anything to be skeptical about.
What if I Want to Solder a Crimped Connector Anyway?
To some people, if the terminal isn’t soldered it just doesn’t feel like a job well done. This is particularly true for people who mostly solder on audio or electronic projects. There, to crimp or solder isn’t even a question. Solder is the de facto gold standard for many applications. Even for me, it took a while to trust crimps instead of soldering. Having done mostly audio wiring, it just didn’t feel right.
However, if you are repairing some high-precision sensor or a component worth the extra effort, you might want to add a dab of solder after crimping. It shouldn’t be necessary, but it shouldn’t harm either (done right). Just make sure the solder isn’t compensating for an inadequate mechanical connection.
To do so, crimp first. Then apply the least amount of solder needed to create a soldered union between the tip of the wire and furthermost end of the connector. That is, you want to apply the solder away from where the wire leads out. The main objective is avoiding solder creeping under the insulation. On open-barrel terminals you might have a bit more leeway since there is a second crimp and a larger distance to the rear end of the connector.
This might be beneficial in that good-but-not-quite-perfect crimp, and can help keep it from moving or pulling through the terminal. If you feel the need to do this I definitely recommend adding strain relief.
What about Tinning Wires?
Tinning a wire consists in coating the exposed stripped end in tin. This is frequently done in electronics to aid with later soldering and to prevent fraying. Whether to do it or not for automotive applications is questionable, at the least.
Per the the IPC (Association Connecting Electronics Industries), IPC-J-STD-001 Rev E, page 13, section 5.1.3, stranded wire shall not be tinned when the wire will be used in:
- Crimp terminations
- Threaded fasteners – terminals which clamp the wire with a screw
- Mesh splices – when splicing wires together
Basically if you’ll be crimping or securing it with a screw in a terminal, you shouldn’t be tinning it. The reasons are two-fold. When the screw closes down on the wire it could break the solder joint making it susceptible to vibration, loosening and corrosion. A second problem is that tin flows slightly at low temperatures which may lead to unchecked loosening later on. I’m sure the fact that introducing less conductive tin in between the copper and the connector doesn’t help either.
Unless you will be soldering the wire to a circuit board later (which can happen, even on a bike – see my decoy alarm project for GPS trackers), I’d avoid it. However, an exception might be if you are still designing and testing a mod and will be disconnecting/connecting the wire frequently. Then I might tin to keep fraying at bay. If that isn’t the case, I’d try to avoid it for this type of job.
I Have to Solder Instead of Crimp – Any Tips?
Okay, so you’ve read all of this, and you are willing to consider it might not be BS. But…you have to fix a problem now and you don’t have time to order a proper crimping tool. Plus, plenty of people solder so it can’t be that bad. What can we do to avoid issues with a soldered connection down the road?
As long as you take the right precautions, of course soldering is good enough for most tasks. The main things to make sure of are:
- Ensure that no solder gets under the insulation – Use the proper tools and technique. Remember, solder tends to migrate towards the heat. And don’t use the soldering iron to directly melt the solder.
- Completely immobilize the soldered section – This is specially important with splices. If done, it avoids the connection work-hardening itself to death. Heatshrink is generally the best solution, as long as you plan in advance. Use two layers or more if needed, and adhesive heatshrink is best since it is thicker. Electrical tape sucks for this job, but you can use it as a last recourse. There should be enough strain relief to keep the joint from moving at all. Of course, avoid using solder unsupported in high vibration applications.
- Solder is not a substitute for a good mechanical connection – Never use solder to hold the wires together. That’s a recipe for failure.
- Use the right size soldering iron – Applying gobs of solder isn’t a substitute for the wrong tool or poor technique. Avoid using an under or over-sized soldering iron. A variable soldering iron is often useful for this reason. If the connection is too large to solder with the tool you have, stop. Crimping or securing with a screw-terminal is probably a better idea.
- Use electronic rosin core solder, and clean later – Rosin core solder helps solder components in less than ideal conditions. That means dirty and oxidized wiring. Since rosin flux only turns acidic when heated, it is typically considered “no-clean”. However, engine bays are hot so I always recommend using some cleaning alcohol in a small squirt bottle to clean off the residual flux. And of course, don’t even consider using acid core plumbing solder.
The key takeaway? Crimp where you can, solder where you have to. Though soldering a wire or connection on a vehicle may make you feel like you are doing a better job, in practice it can cause more issues than it may avoid. To crimp or solder will be a personal decision based on experience, tools and preferences, but in general crimping should be the go-to option. All in all, I’d prefer a good solder over a bad crimp, but a good crimp over either. On vehicle repairs, at least.
At the end of the day, whether to crimp or solder and how you decide to work is up to you. This is just food for thought for the avid DIYer, and I can only hope that it provides you more context to better make that decision yourself.
Got a whole different opinion altogether? Got any tips or suggestions? Feel free to leave them in the comments below.