Properties of wire used in harness?

I'm contemplating one of those things that might make me a hated PO some day. As I am refurbing under the hood of my '74 Midget, I'd like to replace some of the electrical wires. Part of it is a few of the wires have pulled off of the connectors, and others looks like over the years they've been stressed enough that they will pull off some day if the wrong thing tugs on them (like an ... owner). I could definitely just replace the connectors, but the temptation is strong to just replace the entire wire. The harness isn't that pretty - I think a PO re-wrapped it at some point.

I actually have access to a lot of heavy enough wire from where I work (big high tech company), and have a hunch it's actually really high quality stuff as it's used for R&D development of equipment. I can't get every little major/minor color combo of the original harness, but certainly can get black, purple, brown, white, green, red, etc.

And that makes me think of rerunning some individual wires, replacing the connectors, etc.

So how do I know if this wire is "good enough"? If I assume it's high quality (insulation won't rot off, etc.), can I go by type (multistrand) and gauge and be confident? And I guess it's between me and my maker (or the next owner) if I don't use a precise blue/brown wire between the headlamp relay and the headlamp fuse and use just blue instead...

A great source for information on wiring for our cars can be found at britishwiring.com.....
they are a great source for parts, wiring, etc.
I have used them and they have excellent quality products.
Scott in CA

I would love to use them. I would love to have more money to spend on my car as well

Most commercial wiring will have a specification printed on the insulation. Sometimes it references the gauge and the type of insulation. You can determine the gauge by overall diameter and count the strands to compare to the original. The early cars had a cloth braid on the individual wires, so I doubt anything made today is going to be any worse than that. Gauge is the most important.

sqbsprite said:

Most commercial wiring will have a specification printed on the insulation. Sometimes it references the gauge and the type of insulation. You can determine the gauge by overall diameter and count the strands to compare to the original. The early cars had a cloth braid on the individual wires, so I doubt anything made today is going to be any worse than that. Gauge is the most important.

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NO Steve that will not work.

What MGNoir will have to do is get the load in amps for each circuit [From the factory Manual] that he wants to replace.
Then using a standard "American" wire table you can select the proper size wire to handle that amount of current.
Be sure you use copper stranded wire and an American fuse table to select the amperage rating of your fuses.

Here is a site that has a lot of good information of wiring and best practices. Much of it isn't applicable to automotive wiring but the methods and math are.

https://www.aeroelectric.com/articles.html#Wiring Techniques

https://www.aeroelectric.com/articles.html

As a (just retired) helicopter mechanic, I done a fair amount of wiring, hopefully most of it quality. Cleanliness is actually the most important. Second, you really to start with quality wire. Your typical NAPA/O'Riley's is not what you really want. The price between really good wire and average NAPA is not a lot , especially when compared to the benefit/grief factor.

Unfortunately there a bazillion specs for wiring, and most are pretty specialized. You can Google "Mil-Spec" wiring and find a vendor in the Piedmont area. But, they are going to ask you a bunch of questions that you won't have any idea about. They also want to sell you large rolls you won't use much of. The local automotive re-wiring shop may be of help, but they buy lots of wire as cheap as they can because they are trying to make a profit, but still want to put out a reasonable product. You may get lucky and find a sympathetic "sparky" that will sell you as small amount of quality wire once he figures out your need.

I would go to your local airport medium to small size airport (not anything-international) and ask which FBO (fixed base operator) does maintenance. Ask to talk to the avionics shop, or at least an A&P mechanic. Tell them your problem, admit you don't know much about wiring, and they will appreciate your honesty.

They will likely sell you some wire by the foot, off a spool. Anything they have for a light single engine airplane is good stuff. You don't want it from the truck shop. You can always use a heavier gauge (smaller number) than required; you just don't want to go to a smaller diameter wire. For small splices/repairs you probably want a few/several feet of 16, 18, and 20 gauge. The heavier the wire (10 - 12 gauge) the less temperamental it is. NAPA stuff is probably fine there.

The same goes for connectors. Pay a little extra for them. You'll spend much more on quality connectors than wire. Most any connector in a 5-pack bag at any auto parts store is not really quality. Ask the A&P mechanic to show you the proper way to crimp the connector. It matters. He'll be glad somebody asked for his expertise.

You really want to use a "di-electric" grease on anything ever exposed to the weather. Permatex makes it and it will be available at most good parts stores. It keeps out moisture, greatly reduces corrosion, and make dis-assembly much easier - you won't pull connectors apart if they separate easily/properly.

Last, don't forget what I said first, and it doesn't cost anything --- Cleanliness is actually the most important.

Good luck, Blueghost.

Keoke said:

NO Steve that will not work.
.

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No argument here. Wire diameter is directly related to gauge even with stranded wire, but it would be tricky to determine just by looking at it unless it is marked. Stranded AWG is specified by the gauge of each strand and number of strands in addition to the overall size. I assumed he knew that load determines the wire size required. But maybe I'm the one confused.

sqbsprite said:

No argument here. Wire diameter is directly related to gauge even with stranded wire, but it would be tricky to determine just by looking at it unless it is marked. Stranded AWG is specified by the gauge of each strand and number of strands in addition to the overall size. I assumed he knew that load determines the wire size required.

But maybe I'm the one confused.

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NO just that info will not solve his problem.

I think most of you have good ideas, but making it more complicated than it needs to be.
Our cars have really basic wiring and the size or gauge of wires is fairly easy to determine.
Sorry if I am going back to englishwiring.com.....but https://www.triumphrescue.com/BritishWiring_oldsite/Comp.htm
and click on the Bulk Wire tab. The information outlines the way to compare English wire size with American wire size and also typical sizes used. IMHO, the wire purchased in a retail electronic, or automotive store should be fine for his Midget. Make sure the terminals are the same, or replace with good quality parts. No it does not have to be the same color as the existing wire from the factory, but do yourself and the next owner a favor by finding and printing a copy of your car's wiring diagram, and noting any changes.
Scott in CA

if I am going back to englishwiring.com
I would love to use them. I would love to have more money to spend on my car as well

???????-Keoke:confuse:

smaceng said:

IMHO, the wire purchased in a retail electronic, or automotive store should be fine for his Midget.

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This kind of depends on your definition of "good enough". I'd have to agree with BlueGhost here. Napa stuff is good enough if all you want to do is get things hooked up. The insulation gets hard when cold and cold flows when hot. For long term durability and reliability better wire is needed. Mil spec Tefzel insulation and tinned conductors may be overkill for a road vehicle, but if you want wire with insulation that wont crack or melt it's what you want. I'd also have to disagree with BlueGhost on the truck shop warning. Some, but not all, truck fleet shops use very good wire and techniques. It may be worth looking for such a shop in your area for wire.

A good selection of different colored heat shrink helps identify wires when working with a limited selection of colors.

Re: englishwiring.com. If I had $350 to spend on the car, I'd just buy a new harness. I don't, so I'm thinking about what I can do myself.

The wire I have access to work is actually very high quality. It's for the R&D department at Hewlett Packard, and definitely not your average auto supply stuff. It's multi-strand copper, in a variety of gauges from 12-18, also in a variety of colors.

One reference I've found that covers wire sizes nicely is https://www.expeditionlandrover.info/Lucaswirecode.htm, which covers British and US standards (strands & gauge), plus amperage requirements.

Re: englishwiring.com. If I had $350 to spend on the car, I'd just buy a new harness. I don't, so I'm thinking about what I can do myself.

OH BOY MGNoir!!!
That is a good one you found.
Now you can match the American wire guages with your cars circuit current loads or just pick a similar wire size to the original Brit wire.

You just saved $350.00-- Keoke eaceful:

Don't forget to get some of this when you're working with Lucas wiring:

https://www.ebay.com/itm/LUCAS-Repl...riumph-BSA-Norton-Matchless-AJS-/201019710089

SaxMan said:

Don't forget to get some of this when you're working with Lucas wiring:

https://www.ebay.com/itm/LUCAS-Repl...riumph-BSA-Norton-Matchless-AJS-/201019710089

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Absolutely---I AGREE---Keoke--LOL

To know if the wire is good enough, it's not the stranding that's most important, its the quality of the insulation itself. You will want either THHN, THWN, or MTW labeling. This is going under the assumption that you will NOT be buying the wire from one of the British Wiring supply sources. If you can find MTW/SIS, use that, but it's probably cheaper to get it from the aforementioned British Suppliers as it is NOT cheap.

THHN, means Thermoplastic, High Heat, Nylon jacket.
THWN mean Thermoplasic Heat Wet Nylon
MTW is Machine Tool Wire.

MTW will have a greater number of smaller strands, given the same wire size.
SIS will have even more strands, with thicker insulation, It is less "formable", but more durable.

Almost all the wiring in the car is 14 gauge. The exceptions are the headlights, where you want no less than 10 gauge, and the started wiring from the battery, where it think its 4 gauge, but use 2 if you can.

Thanks for the info Bill. I always wondered what those designations meant but was too lazy to do the research, I guess. Anyway, I still would just use British Wiring or Rhode Island Wire to get the proper stuff, fittings and all. BTW, I believe either of them will sell wire in as little as 1 meter units so there is really no reason to "break the bank" to replace everything under the bonnet.

You are correct they will supply wire by the meter so you can keep color coding correct.

Bill L. - The insulation types are exactly the kind of information I was looking for but didn't know how to ask for. Will AWM cut it? From a few brief reads, it seems like it's the same sheathing, but AWM actually has a higher voltage rating.

Ahh on further reading it looks like AWM isn't rated for oil and coolant exposure.