Wiring Practices

[Eneto-55]

There is an interesting article on Hemmings dealing with how to splice wire.

 

Which Wire-Splicing Method Is the Strongest?

 

The article is interesting, but while it deals only with splicing, the comments have some very helpful information (at least in my estimation) that go on into crimping practices, wire wrapping practices, etc.  I have copied some comments into a Word document, and may (as I get time, and if there is interest) post some excerpts. 

[Sniper]

Been doing this kind of thing since 1984.  When the Navy taught me how to do a mil spec connections it was crimp, solder, heat shrink and strain relief.  For splices it was linesman, solder, heat shrink and strain relief.

 

Without strain relief you get wires cracking, soldered or otherwise.  Especially solid core wires, followed by coarse strand wire, then fine strand wire.

[Eneto-55]

27 minutes ago, Sniper said:

Been doing this kind of thing since 1984.  When the Navy taught me how to do a mil spec connections it was crimp, solder, heat shrink and strain relief.  For splices it was linesman, solder, heat shrink and strain relief.

 

Without strain relief you get wires cracking, soldered or otherwise.  Especially solid core wires, followed by coarse strand wire, then fine strand wire.

What did you do for strain relief?  I know what you're supposed to do where a wire goes into an appliance box for strain relief, but what would you do in the case of a splice somewhere in the middle of a wiring harness?  (I spliced my wires years ago, but now the rest of it has deteriorated to the point that I'm going to replace it all with new wire.  So it's a sort of "academic question" for me - I don't expect to need to know, but I'm rather curious anyway.)

[Sniper]

Depends on the specifics, but generally a bundle of wires, tied/taped together is a form of strain relief.  Clamping the bundle to a stolid base with an adel clamp or a zip tie and mount is another.  That corrugated plastic wiring loom is another.   

 

Generally when I was doing repairs in the Navy I just used the already designed strain relief setup. 

[Plymouthy Adams]

3 hours ago, Eneto-55 said:

What did you do for strain relief?  I know what you're supposed to do where a wire goes into an appliance box for strain relief, but what would you do in the case of a splice somewhere in the middle of a wiring harness?  (I spliced my wires years ago, but now the rest of it has deteriorated to the point that I'm going to replace it all with new wire.  So it's a sort of "academic question" for me - I don't expect to need to know, but I'm rather curious anyway.)

I can just see deer in the headlight stare of someone here packing a stuffing tube on a car firewall....

[Racer-X-]

For wiring, I generally follow the standards and practices in this document:

 

https://nepp.nasa.gov/files/27631/NSTD87394A.pdf

 

Before I started following that document, I did my electrical work to the specifications, standards and practices of a certain airline's (a now defunct airline) manual for their aircraft maintenance electricians.  I only have that book in hard copy format, so I can't link to it.  Much of the information and many of the standards are  identical to or very similar to the NASA standard's I linked to.

 

For me, I strongly prefer crimped terminals in connectors.  Where a splice is necessary, I strongly prefer soldered splices.  Most often, I use a lashed splice like section 19.5 in the NASA standards document. The big key with soldered splices is that the soldered section is harder and more brittle than the wire. It seems counter-intuitive, but it's necessary to keep that section as short as possible. The NASA standards are that the spliced area where the wires are in contact and soldered together should be at least 3 times the wire diameter, but never more than 6 times the wire diameter.

 

One other crime against reliability that I often see is when there are several splices in a harness of wires that are bundled together.  When you have to do that, always stagger the splices so that at any point along the bundle, only one splice is present in the bundle. That's also covered in the NASA standards.

 

My own experience is that "lineman's splices" AKA "Western Union splices" are not as reliable in environments prone to vibration and movement. They tend to get brittle, fatigue and crack and become unreliable.  I saw someone mention those here.  They do look cool.  If you must use them in an automotive environment, they need to be in a well supported bundle of wires between secure tie-down points to minimize movement and vibration.

 

If you do use crimped connections, use good, high quality crimpers.  Proof test several test crimps and make sure your crimps hold together under the weight/force shown in table 12-1 in that NASA document.  The forces your crimp should hold to are higher than you'd think. You should also destructively test a few crimps and compare the results to the pictures on that page. They should break in the "preferred" ways.

[Eneto-55]

1 hour ago, Racer-X- said:

For wiring, I generally follow the standards and practices in this document:

 

https://nepp.nasa.gov/files/27631/NSTD87394A.pdf

 

I didn't "study" the document (all 101 pages), but noted some things I typically do that are apparently no-no's, like twisting the strands tighter than their natural "lay". 

One question I posted on the Hemmings site is whether an untinned wire should be tinned before crimping.  What are your thoughts on this?  (If this document mentions this as either advisable or not, I didn't catch it.)

re: soldering a crimped connection:  I have often done the above (tinned a stranded copper conductor prior to crimping).  Also, I usually solder at the cut end of the wire where it is exposed at the terminal end.  (That is, not at the wire end, where it can easily wick under the insulator.)

re: lashing:  I've neither heard of, nor seen this before.  I can certainly see the advantages, because it is difficult to keep two wires tightly against one another while soldering, especially if they are not twisted together, which this document considers a bad practice (if I understood correctly).

re: using unlike terminal connectors where two wires terminate at the same location:  It's obvious that Chrysler didn't do this, as there are often multiple barrel ("bullet") connectors in the same area (especially under the dash, where the main harness connects to the rear harness, that continues to the rear of the car).

re: staggering soldered repairs in a multiple conductor (wire) harness:  This is certainly logical, and this is what I've always done, for the reasons given in the document, basically a "cosmetic" or appearance reason.  But I've wondered if it might have some negative results in that it creates a longer stiff section in the harness, which would seem to increase the likelihood of wire fatigue and breakage, due to any flexing, or vibration.

[Sniper]

NASA, the military and the aircraft industry have different priorities than Chrysler.  Which is why you see Chrysler do things that are contraindicated by the others.  Chrysler needs to build to meet warranty and price considerations, the other have to build to human life considerations.  You get an electrical failure due to lesser quality work in NASA, the shuttle blows up, airlines and a smoking hole appears in the ground, the military and a battle can be lost. 

 

Three is a reason aerospace and military stuff costs as much as it does, it's as close to bullet proof as we can make it and it's tested to prove it so.  Chrysler could do that, for about 3 cars then go bankrupt because no one would buy them because of the price.  Doing it yourself, well the cost is mostly in labor which you are providing for free.  I, myself, would rather invest a couple of extra hours in my garage being finicky about my work than on the side of the road in a pouring rainstorm trying to tie my wiper linkage together so I can get home (BTDT). 

[Plymouthy Adams]

lets be realistic in our comparisons, apples and orange and decades have since past...the modern car industry with the buss systems are enjoying the the ridicules poor ole Lucas got with his daisy chain.....grounds are 90+ of all electrical failures in majority of modern cars....others suffer from poor quality components to start with and all are trying to garner a higher price for their products so many corners are cut.....besides very few cars today will be around in the future compared to what we are calling vintage cars.  They will often be referred to only as vintage photographs...

[Racer-X-]

18 hours ago, Eneto-55 said:

One question I posted on the Hemmings site is whether an untinned wire should be tinned before crimping.  What are your thoughts on this?  (If this document mentions this as either advisable or not, I didn't catch it.)

For me that's a maybe.  Along with the question of whether to solder a crimped connection.

 

If the crimp connector is tinned, I'll usually tin the wire, crimp it, and then heat the joint up from the end of the wire (like you suggested) until the tinning on both pieces melts and melds together. Typically I use tinned crimp on ring terminals and handle them that way. For most "weather pack" and similar connectors, I don't tin, nor do I heat and solder the pieces.

 

Oh, and if the connector (ring terminal or whatever) is tinned and it has some kind of plastic insulation on it, I always remove the insulation and I always use heat shrink in place of the (usually colored) insulation that came on the connector.

 

18 hours ago, Eneto-55 said:

 

re: staggering soldered repairs in a multiple conductor (wire) harness:  This is certainly logical, and this is what I've always done, for the reasons given in the document, basically a "cosmetic" or appearance reason.  But I've wondered if it might have some negative results in that it creates a longer stiff section in the harness, which would seem to increase the likelihood of wire fatigue and breakage, due to any flexing, or vibration.

That type of splice shouldn't be in a section that flexes or vibrates, it should be in a section that's supported at both ends, hopefully to fixed positions. If I'm replacing wiring at a connector using a "pigtail," I'm always try to harvest one from a pull it yourself yard, and run the wiring all the way back past the first tie down/support. If the termination is old, corroded or broken, I take some extra so I can crimp new termination on the end with the connector.  If it's something old and/or rare, and I can't harvest one, I make what I can with new wiring and try to match wire colors as close as possible.

 

3 hours ago, Sniper said:

NASA, the military and the aircraft industry have different priorities than Chrysler. 

I agree.  And I guess maybe I should share the story of how I got on the aircraft spec/NASA spec wiring. 

 

Back in the mid to late 1980's, I used to race sports cars with the SCCA in the southeastern US.  There was a group of us, typically 5 to 7 cars, with driver(s) and a few floating "crew" guys who traveled together and paddocked together. We'd help each other out, and for the "endurance" races, we might team up together to run a car or a few, not all of them, so we'd have "relief drivers" available.  That was mandatory in the races longer than 3 hours, and just a good idea in the shorter 2 and 3 hour "endurance" races.

 

These were mildly modified race cars based on production street cars.  Some "Improved Touring," and some prepped beyond that to "production" or "GT" rules. Nearly every race weekend, there would be one guy chasing some kind of electrical gremlins in his car. It was a different guy, different car most weekends, but the problems afflicted almost all of us. Most of us would try and help out and find the source of the usually "intermittent" problem that either killed the thing or made it run poorly and cut out. There was one guy in our group who never had any electrical issues with his car (and rarely even tried to pitch in and help out).  One day I asked him what the deal was with his car being so reliable and never having problems (hoping not to jinx him).  He explained that his day job was aircraft maintenance (mechanical) for an airline (I actually knew that), and whenever he needed any electrical work done on his race car, he had one of the service/repair electricians from work come to his shop in his basement and help him or just do the electrical work on his race car. Well, I eventually met the electrician and had him come look at my race car and tell me what I needed to do to make it as reliable as the other guy's car. Basically, he told me I'd have to rewire the whole thing.  Actually he told me he'd have to rewire the whole thing and do it "like they did things at work, on the big jets."  Several cases of beer and several steak dinners later, we actually did completely rewire my entire race car, and he taught me how they did it on the big jets.  He even gave me a copy of their manual when a new edition came out one year. After that, I almost never had any electrical gremlins in my race cars. Since then, I've been a believer in those standards.   My old book from that airline is a bit shop worn and outdated now, and about 10 years ago or so, I discovered that NASA document online, which cover the same basic standards and practices with a few minor differences, and when anyone asks about this topic, I refer them to that.

[kencombs]

Commercial aircraft level wiring is (or was when I was around it daily) almost exclusively crimped connectors.  Not because they are necessarily better, just that they work and can be duplicated every time by any electrician/mechanic using the standard tooling and materials.

 

I started with an airline, not as a mechanic but with them everyday, back when all the wiring was tied in neat looms with waxed linen thread.    That is a real sight to see, many, many wires neatly bundled and paralleled so that a wire can be traced end to end easily.  The threads perfectly spaced and tied.

[Eneto-55]

One thing I mentioned above from the NASA document that was a surprise to me, was to not twist the strands tighter than their natural "lay".  As far as I saw, they didn't give a reason for why one should not do this.  (It sure makes it easier to get the wire into the connector, and prevents the end from getting really big if you are tinning it.)

 

Oh, and a tool related question:  What is a quality brand/model of barrel/bullet style connector ratcheting crimp tool?  (For the type of connector used originally on our vehicles.) 

 

I can see that some types of modern connectors may have advantages over the original style, but the housings for these may not easily fit through the restricted passages where the wires pass through, like through the A pillar & to the rear overhead, and also through the A pillar on the right side, to the cabin interior light switch on the Special DeLuxe model.  They can also be a real pain to get the female connectors out of the housings if you need to remove them in order to get the wires through.  (And, hopefully without spending a fortune.  For instance, I use a special crimping tool to build computer cables, to crimp the tiny connectors that attach on a computer board's header pins.  A new one like this tool runs over $1,300.00.  I cannot afford to spend that kind of money on this deal.)

Edited November 22, 2021 by Eneto-55