Why you should NEVER solder wires on your car.

After years of being an automotive technician I have plenty of horror stories of bad automotive wiring fixes. In this video I aim to help anyone that finds themselves in a place where they need to repair a wire on their car.

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Products used in video(paid links):

Wire Strippers:

Soldering iron:

Closed barrel crimpers:

Closed barrel heat shrink butt splices:

Single process open barrel crimpers:

Multi process open barrel crimpers:

Open barrel terminal kit:

Heat shrink kit:

[SteveWhiteDallas]

A good crimp junction is better than a bad solder joint.
I like to solder sometimes, but on somethings, I would rather crimp. I know that experienced technicians know how to make a good solder joint. They know what size solder to use (including core type and percentage) what size iron or gun to use and how hot it needs to be. If you get all those right & tin the wires before connecting them, there will be no need to twist them, and being pre-tinned will mean you don't have to add as much solder when making the joint, which means less time with the iron on the wire. More surface contact between the tip and wire decreases time also. Beyond that, aluminum makes the best heat sink. It conducts heat very well, but doesn't hold the heat very long. But, everything between the iron and the heat sink will get hot, so moving them to the end of the insulation will also deter the solder from creeping up the wire.
HOWEVER, it's very likely that most DIYers are not going to have the soldering skills of an experienced A/P mechanic, or electronic technician. Crimping can be mastered much easier and quicker than soldering, which makes it the best option for most people.

[michaelhope]

As an ex Air Force missile technician I was trained to solder to NASA HRHS (High Reliability Hand Soldering) technique. You can crimp all you want I will continue to solder without failure.

[mechlabman]

I am 74 years old. I built my first crystal radio at age 8. I have spent my entire life in consumer and industrial electronics. I solder EVERYTHING. I usually even solder crimp terminals. If you are having problems soldering items together, use the best solder, always use solder flux, always prepare the work target-wire-terminals-get them clean and shiny. Use a good clean soldering iron ( or gun, love my 25 year old weller gun for big stuff ). Don't rush an iron, let it get to temperature. Always remember you are soldering the wire, not the solder. The objective is to get the work piece hot enough to flow the solder onto it. Learn how to solder.

[philmann]

Nearly sixty years ago, my Dad taught me how to solder. He'd been a radar technician on a carrier in WWII and learned the importance of making a strong mechanical connection before actually soldering. Admittedly, warship techniques may be overkill for ordinary work, but I've never had a proper solder joint fail, which is more than I can say for crimp connections.

[jeffryblackmon]

In the aviation electronics industry, we were taught (as inspectors) to be aware of solder migrating under the insulation, for the exact reasons you stated- after some vibration, the wire will break. Good video! Thanks.

[pmdoit]

As a 40 year electric forklifts mechanic I soldered connections for used in all kinds of corrosive environments. I never had a failure as opposed to some of my counterparts who relied on crimp joints that saw failures. Properly soldered and installed wire connections will not fail. Crimped connections also fail due to heat from bad connection.

[marcseclecticstuff]

Man, I've been doing it wrong for 50 years. Thank you for your insight and showing me the error of my ways. In a prior life I used to do mobile electronics installations (audio, 2-way radio's) and I soldered all wiring under 16ga. The technique I always used was to clean/flux/tin the wires, apply heat shrink tubing to each individual joint, and if possible, another larger piece of tubing over the entire cable, lay the wires parallel (never twist - makes the joint too large), solder them together with LEADED solder - no-lead solder is a lot more brittle. Rinse/repeat for all the other wires, apply dielectric grease over the joints, slide the HS over the joint & shrink with hot air - NEVER use an open flame. The excess grease should squeeze out the ends. Once all the individual wires have been soldered/greased/shrunk then apply an additional layer of dielectric grease over/around all the splices, then slide the outer tubing over the repaired area and shrink that down. If it's in a harness, I still pack the joints with grease then use high quality electrical tape over the entire harness to help protect the joints. For wiring that's more exposed, I'll use 3M mastic tape instead of electrical tape for addition protection. I've found that it works better if I heat it up with my heat gun before applying it. Once the repairs are complete, I use plenty of wire ties to mechanically secure the harness from flapping in the breeze to prevent stresses on the wiring to concentrate at the joints. If it's just a few wires I'll take a bit of larger, solid wire and tape it parallel with the wire(s) extending past the joint on both sides to provide mechanical support and prevent any flexing @ the joints. I've done thousands of joints on cars, trucks, boats, trailers, motorcycles, mowers, CNC forklifts, machining centers etc. using these techniques and as far as I know, not a single joint has ever failed. To be clear, I use crimp connectors & ferrules all the time, but usually when it's in a dry environment, and typically to terminate wiring, rarely for splicing.

The bottom line is it doesn't matter if you crimp or solder the connections as long as you do it correctly. Just because a lot of folks do it wrong doesn't mean you should "NEVER" do it as you imply. In fact, in the 50 years I've been working on things, I've had several orders of magnitude more issues with people's crimp connections than I have soldered ones. If you do nothing to protect the joint from the elements, a crimped connection will fail quicker than a soldered one due to moisture ingress and corrosion. This is especially true up here in the north where tons of salt is dumped on the roads in the winter. I've seen exposed crimped connections fail in less than a year due to salt corrosion. Crimped connections do tolerate mechanical stresses better, but again it's down to proper technique and providing mechanical support. But the most often missed step on exposed connections is dielectric grease. I don't think I've ever seen anybody doing 'repair' videos use it. I see some folks like this video advocating adhesive lined shrink tubing and it's certainly better than nothing but not something I'd recommend. Besides being a lot less common and more expensive than plain HS tubing, it's only going to be effective if your wiring is clean, and only if it's a single, individual wire that the tubing can shrink completely down to without any gaps. Too often I'm doing multiple wires or different sized wires where I won't get a complete seal with the tubing. If you use dielectric grease then it doesn't matter if there's any gaps, the grease completely fills the voids when it gets shrunk down. The butt splice connectors that come with DE grease and shrink tubing that you showed are pricey, but the best alternative for folks that don't do this sort of work often.

[kirkdarling]

You're making soldering sound harder than it really is. It's not "rocket surgery." In my 60 years of doing radio building, I've never heard anyone who knows how to solder claim that any kind of crimping is ever inherently better than soldering. Quicker, yes, easier, yes, "good enough for the purpose, " maybe; but inherently _better?_ Never.

[ronaldbarry]

I’ve been an industrial robot technician for over 30 years. They move and vibrate on top of hard running machinery 24/7. We crimp connector pins because that is what they are designed for. For every other in line type wire connection we solder. I have never had or seen a properly soldered connection fail. NEVER. I have seen dozens of crimps fail.

[floorpizza]

While your soldering joint is OK, a couple of tips...
1. Use flux. Liberally apply flux to the wires before soldering. The rosin core of your solder isn't enough.
2. Twist the wires into a Lineman's Splice before soldering. The Lineman's Splice is stronger than the wires themselves. This step insures that there is no way the splice will fail before the wire will. Adding the solder to the Lineman's Splice will aid in lowering electrical resistance. Adding this step to your soldered wire joints is a complete game changer, and it is not difficult to do.

Using flux, a Lineman's Splice, and solder will result in a joint with less electrical resistance than any crimped solution out there, and far stronger than crimping.

And it might very well be over kill. There's nothing wrong with a properly crimped joint, either. This is a situation in which there is no real "correct" answer. Properly soldered or properly crimped is just fine for automotive electrical work, as long as either joint type is done correctly.

Source: I'm 56 years old, and have been soldering and/or crimping wiring harnesses on a wide variety of things... cars, trucks, tractors, trailers, RV's since I was 16. I have also done a lot of car audio installations. While I do stand by my above statement about there being no one "correct" solution, there is an exception to that rule: I *always* have and *always* will solder connections for car audio or alarm system installations to achieve the lowest electrical resistance possible across a joint.

[KentuckyRanger]

I worked for a company, that manufactured control computers, for nuclear reactors.
We had a meeting about crimping vs soldering.
It was determined, that twisted pairs need solder with moisture barrier heat shrink, and that crimp connectors should also be soldered, for redundancy.
I was part of that team, and was the one who suggested these processes.
DIY crimping, over time, will work the mechanical connection loose, causing connection issues down the road.
"But Ranger, all connectors in plugs used in vehicles are crimped!"
True, and most will last the lifetime of the vehicle, but some don't and need replacing.
Any mechanic with a year or two under their belts will tell you stories, of how multiple wire connector plugs, have needed to be replaced, from mechanical failure.
In fact, a good mechanic, knows how to replace the one or two bad pins, instead of the entire connector plug.

[Quiet-storm]

Take it from an Engineer who worked for a company that makes terminals for the automotive industry. A solder joint is superior to a crimped terminal which is done by a machine. In testing, over time and in different environments the crimped joint will have a voltage drop, meaning the resistance begins to increase till failure occurs. A solder joint is literally good forever. Now you throw in people that crimp as a diy project and the quality of any of these crimps will be less then desirable. In an outdoor environment they will usually fail quickly.

[pfuller]

Having over 40 years experience working in electronics and being a backyard mechanic I think the most important message you could give would be that you should do what not only works best for you but has the best chance of long term success. There are places I wouldn't trust solder, and for simplicity a lot of my work uses a good quality heat shrink crimp. But anything I can bench I still prefer to use solder.

[AutoBat]

Don't forget to put the heatshrink tubing on BEFORE you crimp! Ask me how I know!

[LTVoyager]

If you wick solder past the wire insulation, it is due to very poor tools and/or technique. This usually is caused by using too small a wattage iron which means you have to heat the wire far too long letting the heat extend well down the wire. It can also be caused by simply adding in far too much solder. A high wattage iron will heat the join area very quickly and the soldering will be done before the heat and solder can wick down the wire under the insulation. And you need very little solder. And if you apply shrink tube to provide some additional strain relief past the insulation, issues with vibration and fatigue breakage simply aren’t an issue. These issues are due to poor technique.

A quick summary:
1. Poor soldering is a bad way to splice wires.
2. Poor crimping is a bad way to splice wires.
3. Good soldering is a good way to splice wires.
4. Good crimping is a good way to splice wires.

I personally like both methods, but use crimping more simply due to its convenience and speed. You can work in the field without need for electrical power of any sort and crimping is pretty fast with the right tools and a little practice. However, if I need a super reliable, super strong and low resistance connection, I will use solder every time.

One thing I have wanted to do, but have yet to invest time in is testing soldered splices vs. crimped splices for both resistance and pull strength. I strongly suspect that solder would win both contests and I saw one YouTuber who did the resistance test and solder clearly won that, but, as I recall, he did not strength test the connections which would have completed the puzzle.

[davidfisher]

The fellow who does a hack job with soldering is also likely to do the same with the crimp. Attention to detail is key with anything and if you don't have that, the end result will be the same.

[Mr.Jaysick]

Thanks for the advice homie!
I’ve connected 100’s of wires working on classic cars over 20 years and if you use good thick shrink tubing, that wire is not gonna bend at the solder point causing a break like you illustrate in my experience. Having said that, sometime I just don’t have the space to solder. If I use a crimp connector, also use good shrink tubing but if it’s on the outside of the car I’ll also add liquid electrical “tape” on top of that. Never had a problem

[helomech]

Been a aircraft tech for 30 years, and that crimp connection will break easier at the crimp than the solder one will. We do crimp on aircraft, but they are environmental crimps with crimpers that are calibrated. I still prefer a good hot solder to any crimp. We used to use those crimps you like on our strobe lights, but got away from them. Failure rate was high. I will never be convinced a crimp is better than a solder. Twist that crimp joint like you did with the solder joint.

[AnthonyJ]

For joining wire ends, crimping makes a ton of sense. For integration I prefer solder since it would require you to cut the factory wire. Different techniques for different applications. Great video!

[jdtractorman]

When I worked for GM, they would include the crimp/seal splices in connector repair kits. They included in their electrical repair kits that were shipped to the dealer with a set of ratcheting crimpers. They work perfect and never failed me once. That's why I bought a pair online from crimp supply. They are a little pricey, but worth the money because of how well they work.