Should I Crimp or Solder Wire Connections?

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.

To Crimp or Solder, What is the right way?

If you’re wondering whether to crimp or solder, ask yourself when is the last time you saw a factory soldered joint on your bike?

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.

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 Better than Soldering?

Crimping is the process of creating a permanent electrical connection between one or more conductors and a crimp terminal in any form. 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 carelessly clamping down a terminal on a wire can’t provide a more secure connection than a terminal lovingly hand-soldered by a careful DIYer? Here’s a few reasons why you should consider whether it’s more appropriate to crimp or solder.

Wire Fatigue

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.

Another factor when choosing to crimp or solder or vehicles is the repetitive wire movement. 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.

Resistance

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 on if it’s better to crimp or solder, consider this. 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 you have used X method for years without ever having a problem. They’ll just crimp or solder depending on if they feel like it or not. Heck, 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.

Wires

Regardless of if you’re going to crimp or solder, it’s important 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. Choose the right wire gauge depending on its length and current draw based on an 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, nylon (the translucent ones) over PVC insulation is a better choice. 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 heat shrink 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.

 Whatever connector 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

Wire Strippers

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.

Crimping Tools

Finally a good Ratcheting Crimper. This is probably the most important component. 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 / 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.

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 die electrical grease 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. It also 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.