In my experience, automotive electrical problems can be amongst the most frustrating to diagnose with loose or faulty connections often being the root cause. However, unlike so many other types of problems that can occur as a result of mechanical stress, driver error, or just plain bad luck, electrical problems can be almost entirely avoided by applying a little bit of knowhow when making connections.
Several years ago, I installed a fuel cell which – amongst other things – involved wiring up an electric fuel pump. For serviceability I incorporated a connector into the design, which involved splicing two wire ends together and applying solder to ensure they didn’t pull apart.
Everything worked well at first but after a while I started experiencing problems with the engine cutting out in the turns (one high speed bumpy turn in particular). My initial hunch was fuel delivery related – which ultimately proved to be true – but the specific cause was time consuming and difficult to diagnose. Random luck helped my find the problem sooner than would have otherwise taken.
While testing a new fuel pump in the workshop I bumped the connector and the pump sputtered. Turning my attention to the connector, I discovered that the soldered connection failed leaving me with two wire halves. The heat shrink insulating material hid the problem from view and kept them mostly in contact with each other but all it took was a little bit of force and/or vibration (like driving over a bumpy turn) to open up a gap breaking the flow of current to the pump.
Like most electrical problems, the fix for this problem was easy once diagnosed but a long an painful journey to get there. Ironically, in my effort to sure up the connection with solder I made it less reliable. Realizing this sparked my interest as to the correct way to make reliable electrical connections.
The topic of soldering versus crimping is often debated. Already, there have been several responses to this article denouncing crimping as the preferred method to soldering. That crimping is a preferred method is my opinion (a generalization for which exceptions apply) and I am in the good company of aerospace, military, Formula 1, and medical. If performed correctly, both soldering and crimping will produce reliable connections. Likewise, if performed incorrectly, both will result in unreliable connections. Hence, there is an abundance on anecdotal evidence for and against each method available on the Internet.
A key and significant advantage of crimping over soldering is the ease and speed with which a properly formed connection can be consistently performed. I have seen far too many people get soldering wrong (also my opinion, MSME & having worked in aerospace too) and hence my motivation for writing this article. With proper tooling crimping is nearly foolproof. There are a wide variety of connector types and associated tooling that range from inexpensive to very expensive, but even inexpensive connectors can produce good results. The tooling and connectors demonstrated in this article are on the more expensive end of the spectrum but the same principles and techniques apply to other connector types as well.
Why soldering is bad
Hopefully your answer to the above question is a resounding no. Ceramic has several properties that when viewed independently make it an excellent choice; however, its low ductility (brittleness) makes it a poor overall choice. Wire must be able to bend freely as it is routed through the car and is subject to constant flex and vibration. When you use solder to make electrical connections you’re also greatly reducing the wires ductility in the solder region and – like a chain – the wire is only as reliable as its weakest link.
If you take the opportunity to inspect the connections made by the manufacturer of your automobile, you’ll discover that most if not all connections do not have any solder applied. The recall cost to an automobile manufacturer for a flawed electrical connection can run hundreds of millions of dollars, so their engineers incorporate only the best practices for forming durable and reliable electrical connections. Think about this the next time you pull out your soldering gun to make your electrical connection super reliable!
The following video illustrates the effects of solder on a wire connection and compares it to a properly formed connection using a crimper.
Thus far the focus has been on reliability as reason to avoid solder but there are other practical considerations as well. Soldering can take significantly more time than crimping (a topic we will get to shortly). For large projects, this can mean added days. It also requires a higher degree of skill to execute properly if used (e.g., not enough heat, wicking past the contact into the insulated area, etc.). For enthusiasts, electrical work is often performed in compromising positions with poor lighting such as under the dashboard, underneath the car, inside the engine bay, etc., which can make applying solder a challenge. Proper ventilation in tight quarters can also be difficult to achieve but is necessary in order to avoid breathing in toxic fumes. Care should also be taken to avoid letting solder (or solder residue) come into contact with the mouth, cuts, and sores. Always wash your hands after handling solder!
I suspect many resort to soldering connections because they perceive crimps as being weak or otherwise insufficient by themselves. A common scenario it to take a crimp-style connector, crimp, and then apply solder to strengthen the connection. However, a properly executed crimp can be as strong as or stronger than the wire itself is properly executed. By adding solder you are ultimately undermining your desire to form a more reliable connection.
You might be wondering why soldering connections is bad when modern cars contain scores of electronic printed circuit boards (PCBs) each having hundreds of soldered connections. Unlike wires being routed throughout your car, the components soldered onto a PCB are not subject to flex and handling because they are mounted to a rigid plan (the PCB board) contained within an enclosure. If vibration is a concern, the PCB it can be mounted on vibration isolators and epoxy can further be used to mechanically secure the components in place. None of this is true for most automotive wiring projects. Furthermore, as with any rule, there are exceptions and the application of solder in forming connections is no exception. Used properly in conjunction with crimping, solder can be used to build a more reliable connection but is unnecessary in most cases and – in my opinion – the risk of getting it wrong does not outweigh the benefits and therefore is not discussed.
If done with care, solder can be applied to a crimp connection as an added measure of reliability by applying only in the area near the very tip of the wire. The solder must not flow into the region below the crimp compression as you want the wire itself to remain flexible so it does not break apart from the connector. In my opinion, the risk of making a mistake is far greater than any improvement in reliability (marginal at best). It also adds a significant amount of time for each connection to be made (2-3 times) and it therefore not advised.
The perception that crimping is inadequate may stem from the commonplace crimper available for about $10 at your local hardware, automotive, or electronics store. This tool has no place in forming automotive electrical connections and if used, adding solder probably will serve to better the connection.
The key to a reliable crimp connection is having the right tool for the job, and knowing how to use it. The right tool depends on the type of connector being used, of which there are many. Even an aerospace quality crimp tool will not work or produce proper results if used on the wrong connector type. Some shops limit themselves to using a small handful of connector types because they don’t want to or cannot afford to purchase tooling for every type. I’m partial to Deutsch DTM style connectors for reasons stated below and which will be illustrated extensively throughout this article. For these connectors, crimp tool like the one illustrated by Figure 5 is required. If you choose a different type of connector, be sure to ask the vendor or do your research as to the proper tooling required and learn how to use it properly.
Tooling and Connector Hardware
Deutsch DTM Connector
- Incorporates circular contact pins facilitating fast and virtually foolproof crimps.
- Wedgelock insert fixes pins precisely in place for smooth and easy plug / unplug action.
- Suitable range of wire sizes (16-22 AWG) for most connection needs.
- Available in 2, 3, 4, 6, 8, and 12 pin connector arrangements.
- Inline and flange mount available.
- Parts readily available from a wide range of suppliers in gold or nickel plated.
- Pins are easily removed from connector housing and can be purchased separately.
- Receptacle and plug assembly halves can be purchase separately.
I order my connectors through Motec USA because they’ve never failed me and they also offer kits that make ordering parts a little easier (housing, pins, and wedge sold packaged together). The kits can be found in the Motec catalog available on their website. For a complete list of distributors in the USA and worldwide, visit the TE distributors webpage. I found the complete Deutsch connector catalog on the LADD Industries website. LADD is a Deutsch distributor.
In addition to complete product line, the Deutsch catalog contains lots of useful information such as produce line overview, tooling, electrical characteristics, operating condition tolerances, and how-to instructions.
With the DTM connectors you can choose solid barrel or stamped pin types. I prefer the solid barrel pins because they result in fast and virtually foolproof crimps. This pins seen in the illustrations are the solid barrel type. Stamped pins have wings that curl onto the wire. Either pin type is fine for most applications. Just be aware there are two different types of pins, each requiring a different crimp tool. Refer to the Deutsch catalog for additional details.
For DTM connectors, I use the M22520/1-01 “large MilSpec crimper” manufactured by Astro Tool (Figure 5), also available from Daniels Manufacturing Corporation (DMC). These cost about US$250 new. You’ll also need to purchase a crimp head (a.k.a., “turret”), which is M22520/1-02 for the large crimper and about US$80 (Figure 9). In all, expect to pay about US$330 new. These are also commonly available on eBay for about ½ the cost, which is how I purchased mine. It sounds like a lot of money for a crimper, but its foolproof design will save you tons of time and you’ll get perfect crimps every time. I’ve used a number of different contact types and associated crimpers and this is by far my favorite, so I seek out connectors incorporating a solid round pin design for all of my wiring projects where applicable.
Like a quality crimper, you’re not going to find Tefzel wire at your local hardware, electronics, or automotive store. You’ll need to order it online but there are plenty of suppliers. I get mine from Pegasus Auto Racing Supplies.
For automotive use, always use stranded wire for flexibility. Solid core wire has no business being in an automobile.
As described in the illustrations below, I use the Ideal Stripmaster wire stripper. It’s expensive but only absolutely required if using Tefzel wire, else less expensive strippers of similar design can be used with good success.
The following steps are DTM connector specific and have nothing to do with crimping. They illustrate pin insertion and connector housing assembly. I’m using different wires (Tefzel insulated) crimped from a previous job so don’t be confused about why not red 24 gauge wires like the ones crimped above.
LADD is a Deutsch distributor.
Be sure to document your pin assignments and save them someplace safe.