Have you ever experienced a tool or machine that did something so well that you would never do it again without the machine? Every subsequent time you reached that problem, you would avoid doing it a less optimal way. This topic is similar but deals with sourcing specialty parts; installing them is less of a challenge.
You might not be able to go back to your old ways ever again.
Let’s start with a description of the problem, which comes in many forms:
- The premade wire harness is too long, so you end up with a coil of wire to keep everything tidy.
- The harness is too short to reach its terminating component.
- A component has some connector built into it, and you are told to just stick spade terminals on your wires and push them on individually.
What’s the big deal? We have all seen these manifest themselves on projects of all types, and everything works fine … but there’s a better way. You can purchase the connector in pieces (plastic housing, terminals, seals, etc.), then cut your wiring to the exact right length and install the connector. Many builders have done this for things like D-sub connectors on avionics, but that is just the tip of the iceberg. There is no excuse for a coil of wire zip-tied up, some makeshift spade terminal connector bundle, or inline butt-splices. If I am successful, then by the end of this article you will share my gag reflex reaction to seeing “pigtails” for sale.
The problem with pigtails is they guarantee that you will now have X amount of butt-splices in your wiring, something you should avoid at all costs just like spliced control cables. They often even come with wire splices! I like to think of wire connections and crimps like fluid fittings. Using a pigtail is similar to having an oil line too short and adding a union fitting with some hose clamps and an extension (which you should also avoid). Fewer joints, junctions, and fittings means fewer chances for failure.
If you find that your CHT and EGT probes don’t come with enough wire to reach the engine monitor, then there are special connectors for thermocouple wires too.
I never liked the idea of premade wire harnesses because they are usually too long or too short, and you are left feeling obligated to use all the pre-installed connectors. A much cleaner install results when you ditch the guilt of cutting a connector off and leave yourself with the perfect length of wire remaining. I would much prefer a wire harness “kit” that simply includes all the necessary connectors and terminals. Of course, this requires more cost in tools, but it is time we bring our wiring skills up to the level of our sheet metal, composite, and fabric covering skills.
Once you embrace that splicing pigtails into wire harnesses is not the best way, you are left with two main challenges: finding the connector parts and crimping the terminals properly.
For finding parts, I will recommend three different companies:
- DigiKey: Good source for industrial connectors like D-sub, MATE-N-LOK, MOLEX, etc. Usually not kitted; you will have to order the housing and terminals separately. Very inexpensive.
- Mouser: Similar to DigiKey but also includes automotive-style connectors. Usually not kitted; you will have to order the housing and terminals separately. Very inexpensive.
- Corsa Technic: Specializes in automotive-style sealed and unsealed connectors. Easy to search and compare pictures. Parts can be purchased kitted or separate.
- eBay: Sometimes after exhausting all options, you can find obsolete or oddball connector kits here.
Sourcing the connectors and terminals is by far the most difficult part of this venture. You may spend hours searching through pictures on Mouser or Corsa Technic until you find the right connector. Sometimes you will be left with two options that look almost identical, and I recommend you buy both to try out. Pretty soon you will start to recognize different Sumitomo and Aptiv connectors out in the wild, at which point you may need to speak with a therapist. Unlike other aspects of aviation, connectors are usually very cheap, sometimes less than $1, and you will often spend more on shipping.
As for installing and crimping, the best part of entering this world is that you will become familiar with the data sheets available on these websites that often supply more information than you need. For example, a data sheet on an Aptiv Metri-pack connector will usually include a drawing of the part with all related terminals and seals listed, and sometimes even the mating connector part number. Some datasheets will be catalogs of all variants of the connector and can specify the crimper required or the crimper settings to use. These vendors often have the crimpers for sale as well. You will quickly become familiar with different types of terminals and corresponding crimper styles to accommodate most things you will encounter.
Key Takeaways
- Never buy pigtails!
- Never use solder, set screw, or crimp butt splices.
- Save weight and avoid extra loops of wire lying around.
- Familiarize yourself with the online sources for connectors.
- Always buy extra terminals so you can practice dialing in the right crimper.
- Perform some pull testing with your crimps on scrap wires of the same gauge.
Remember that clean wiring is often a thankless and laborious task, but know that you will have fewer chances for wire fatigue and failure and better odds of troubleshooting and amending wiring in the future. The skill of sourcing and installing connectors transcends aviation and will come in handy with any project involving electricity.
Lots of good advice, Troy, but I’ll take exception to your comment on soldering. A properly done and properly supported soldered connection is sometimes the best option. Many year’s ago I had to complete a course to become NASA certified to create and work on soldered connections, and so I’d tell ‘ya that if it’s good enough for satellite equipment, it’s good enough for your homebuilt. Beyond simply knowing how to solder, there are two minimal requirements; first, a solid mechanical connection (a lineman’s joint), and second, support for the soldered joint within an inch or two on either end to prevent vibration related mechanical fatigue.
A properly done soldered joint takes less space and likely weighs the same or less than a crimp type connector. Don’t be afraid of them!
Yeah — soldering should NEVER be done for mechanical strength; only for electrical veracity.
Thank you for extending the conversation! Solder definitely has its place, and I am sure you are aware of the many “solder cup” varieties of connectors, which work great when strain relieved properly.
“Many year’s ago I had to complete a course to become NASA certified to create and work on soldered connections”
Solder is nice. Very nice. And if you’re NASA certified, go for it. But solder brings with it a lot of variables. Hence the need to be certified.
You’ll find few soldered connectors on military aircraft. Most are crimped. Simple, repeatable, and I’d argue fewer variables. And, much easier, especially if you need to re-pin or change out a connector.
A good system (pick your poison and stick with it), use the correct crimp tool and die, and you’ll have secure, repeatable results.
And don’t forget the insertion and removal tools. You’ll put the wrong pin in the wrong hole eventually, and the correct removal tool will help keep your sanity.
A little too long is way better than too short. Great article (hate hate hate butt splices), but I always leave some service loop (or length) so I get that box out of the panel far enough to disconnect it. And I pull test every crimp – it is cheap insurance.
Butt connectors are good, you just have to know how to use ’em. Take the two or more wires you wish to connect, twist them together, insert them in one end of the connector and then crimp them correctly. Always leave enough extra wire to allow a clip off disconnect and then a reconnect. If you really want a good connect then solder it correctly and forget it. You do need to learn how to solder correctly and know what looks like a cold solder joint. Hence the need for extra wire for the connection. Plastic moulded connectors are O.K. if they are installed expertly but can become intermittent with age and stress like most of us. Stick with solder.
Troy, having dealt with a number of crimpers, connectors and the things they crimp. I learned a lot (hopefully correctly) when I upgraded my panel to a Dynon Skyview HDX was wondering if you could do an article on crimpers and the terminals they crimp. This, I think was one of the hardest things I had to learn in my upgrade.
That is a great idea, I can help shed some light on the topic of crimpers and terminals!
Great stuff, Troy!
Adding to the list you shared above, I’ve used the Deutsch DTM series for some areas of my Bearhawk build.
For sourcing, I found that Del City (delcity.net) had better pricing than DigiKey for many of the Deutsch parts.
Great topic! Surprisingly I would add Amazon to that list of suppliers as I have had pretty good success there lately. They tend more towards kits than individual pieces though. I do tend to hit all my connections with a soldering iron, just be careful to include stress relief (the smaller the wire the more critical this is and aircraft wiring has lots of small wires). I DO use a LOT of heat shrink tubing. Get the better heat shrink with adhesive inside for best results. As mentioned de-pinning tools/skills are a MUST for working with connectors. And last bit: those thermocouple connectors come in 3 different temperature ratings and the most common low temperature (as shown) are NOT suitable for engine compartment use.