Wiring Harness Best Practices

[The Dark Side of Will]

Do you have experience with high temperature cloth or rubberized cloth tape?
BMW uses some types of that on their hoses and harnesses with good success after 30 years.

e.g. a product like this: https://www.amazon.com/dp/B07HHQNNV9/



I wouldn't use that particular product as the grammar mistakes in the description make it obvious the supplier is "off-shore", but I'd certainly appreciate if you have a recommendation for a good quality domestically available product.

[The Dark Side of Will]

Also, the outfit that used to make the 4.9 harnesses for The Fiero Factory was Injection Technology. Their website is gone now, so I guess they're closed. They used shrink tubing to dress their harnesses.

There are various shapes available in shrink tubing:

https://www.galco.com/buy/HellermannTyton/422-40000



https://www.nelcoproducts.com/store/hea ... hapes.html



There are also dressing methods to be borrowed from aerospace harness dressing which can use straight shrink tubing in Y's.

Do you have much experience with shrink tube?

[The Dark Side of Will]

Ahh... here's the product that claims to be BMW/Mercedes/Audi harness tape:

https://www.amazon.com/dp/B00EH6IZ6Y/



ETA: MFG's page: https://www.tesa.com/en-us/industry/tesa-51026.html

https://www.tesa.com/en-us/industry/aut ... harnessing

Sorry... not intending to thread-jack... I just have a harness build coming up and want to figure out what I'll be using to dress it.

[pmbrunelle]

Yes, I have used Tesa 51036 fabric tape extensively on the White Bug's engine harness.
viewtopic.php?f=3&t=6195&start=140#p159404

Oftentimes, I just wrapped it around the ends of split loom, to prevent the loom from slipping off the bundle radially. I also used the tape to hold the harness together prior to split loom installation (imagine like a broccoli elastic, with a spacing every 3-12 inches).

On my project, you can see I generally made half-pipe brackets to support the harness (covered with split loom):
http://www.fiero.com/forum/Forum2/HTML/142133-2.html#p60
After sandblasting and painting, I used two strips of Tesa 51036 to secure the harness to the half-pipe.

I don't like wrapping very long continuous spirals, because if you ever have to service the harness, it's far more of a PITA to have to unwrap everything. For some short runs I used the Tesa 51036 exclusively without split loom.

The factory at work actually keeps Tesa 51036 in stock (among other tapes). The wire harnesses they build are mostly for buses. I decided to try what the factory used on my personal car, and I am satisfied with it.

As I understand it, 51026 is an older model that has been superseded by 51036. However, being a good supplier, Tesa didn't pull the rug from underneath existing happy customers. Don't piss off current customers by changing things when they're perfectly happy with their tested and reliable solution.

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Use nylon split loom, not polyethylene. PE won't handle engine bay heat. Nylon typically has a white stripe running down the side. To avoid buying entire new spools for short segments, I raided cars at the u-pull, and then thoroughly washed (hot water + oven cleaner) the split loom. If the split loom was on an engine, you'll probably be OK.

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I didn't know about those heatshrink connectors. Looks like they're intended to be used with flexible PVC wire sleeves. PVC wire sleeves are more "Japanese-style". I guess if the heatshrink connectors come in an adhesive-lined version, I would suggest that so they remain stuck to the PVC wire sleeves.

The harness-building method I am familiar with is to build a full-scale pegboard, and then lay the wires onto the pegboard. Pegs determine the locations of various tap-offs. Once the wires are laid out, the harness is then wrapped/covered at the next station.

Having to slide all the connectors and tubes does not seem compatible with the pegboard paradigm of harness-building.

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For your harness, you should know how to do wire splices; I'll post later on that subject.

I guess I should also say a word or two on SAE J1128 wire, and anything else that comes to mind.

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Maybe you can split off the "wiring best practices" posts into its own thread, and clean up this thread and keep this one the PVC tape comparison?

[Honest Don]

Also, the outfit that used to make the 4.9 harnesses for The Fiero Factory was Injection Technology. Their website is gone now, so I guess they're closed. They used shrink tubing to dress their harnesses.

There are various shapes available in shrink tubing:

https://www.galco.com/buy/HellermannTyton/422-40000



https://www.nelcoproducts.com/store/hea ... hapes.html



There are also dressing methods to be borrowed from aerospace harness dressing which can use straight shrink tubing in Y's.

Do you have much experience with shrink tube?

That’s cool stuff! The “request quote” button always makes me a bit uneasy though.

[The Dark Side of Will]

Yes, I have used Tesa 51036 fabric tape extensively on the White Bug's engine harness.
viewtopic.php?f=3&t=6195&start=140#p159404

Oftentimes, I just wrapped it around the ends of split loom, to prevent the loom from slipping off the bundle radially. I also used the tape to hold the harness together prior to split loom installation (imagine like a broccoli elastic, with a spacing every 3-12 inches).

On my project, you can see I generally made half-pipe brackets to support the harness (covered with split loom):
http://www.fiero.com/forum/Forum2/HTML/ ... 2.html#p60
After sandblasting and painting, I used two strips of Tesa 51036 to secure the harness to the half-pipe.

I don't like wrapping very long continuous spirals, because if you ever have to service the harness, it's far more of a PITA to have to unwrap everything. For some short runs I used the Tesa 51036 exclusively without split loom.

The factory at work actually keeps Tesa 51036 in stock (among other tapes). The wire harnesses they build are mostly for buses. I decided to try what the factory used on my personal car, and I am satisfied with it.

As I understand it, 51026 is an older model that has been superseded by 51036. However, being a good supplier, Tesa didn't pull the rug from underneath existing happy customers. Don't piss off current customers by changing things when they're perfectly happy with their tested and reliable solution.

Good to hear that about Tesa.
They also now have wide versions of the tape to use to wrap the harness lengthwise, like adhesive split loom. Looks handy.

Use nylon split loom, not polyethylene. PE won't handle engine bay heat. Nylon typically has a white stripe running down the side. To avoid buying entire new spools for short segments, I raided cars at the u-pull, and then thoroughly washed (hot water + oven cleaner) the split loom. If the split loom was on an engine, you'll probably be OK.

I'm aware of nylon vs. PE. I'm not a fan of split convoluted tubing, though. It provides abrasion and some heat protection, but in order to keep grit, dirt and oily scunge out of the wires, the harness still has to be wrapped underneath, and the split loom has to be secured at the ends and branches as you mentioned. This makes it more labor intensive to use compared to some alternatives.

I didn't know about those heatshrink connectors. Looks like they're intended to be used with flexible PVC wire sleeves. PVC wire sleeves are more "Japanese-style". I guess if the heatshrink connectors come in an adhesive-lined version, I would suggest that so they remain stuck to the PVC wire sleeves.

I haven't messed with Japanese cars much, but BMW and Audi like to fully encapsulate their harnesses. There are plastic boxes that have grommeted holes where harness sleeving fits the grommet and at the other end of the sleeving, shrink tube connects the sleeving to the connector body... so the wires--at least the important ones--are almost never actually exposed to the environment. I guess that's desirable when your soy insulation tastes good to rodents.

The harness-building method I am familiar with is to build a full-scale pegboard, and then lay the wires onto the pegboard. Pegs determine the locations of various tap-offs. Once the wires are laid out, the harness is then wrapped/covered at the next station.
Having to slide all the connectors and tubes does not seem compatible with the pegboard paradigm of harness-building.

I've built one on a peg board... peg boards take up a bunch of space. I always figured that a small shop that built a few of one type of harness, then a few of another type of harness would have a reconfigurable peg board with holes on a 1" grid... then just have a drawing as part of the production package that lays out where to drop the pegs in and where the harness branches go.

I spoke with someone at EFI Connection years ago. He said their design documentation and wire lengths were good enough that they used the length of the shrink tube to define the distances between branches. I'm not sure what, if anything, they used to cover the joints. Maybe the distal shrink tube was long enough that it had to insert into the next proximal piece in order to ensure complete coverage. This method only allows parallel Y branches, so be careful with routing.

For your harness, you should know how to do wire splices; I'll post later on that subject.

I guess I should also say a word or two on SAE J1128 wire, and anything else that comes to mind.

I've been using butt crimp splices with clear shrink tube, and mostly CarQuest automotive wire. How big a difference is there, really, between the right size of "dry" shrink tube and adhesive lined shrink tube in terms of water infiltration?

Maybe you can split off the "wiring best practices" posts into its own thread, and clean up this thread and keep this one the PVC tape comparison?

Done

[pmbrunelle]

I've been using butt crimp splices with clear shrink tube, and mostly CarQuest automotive wire. How big a difference is there, really, between the right size of "dry" shrink tube and adhesive lined shrink tube in terms of water infiltration?

In automotive normal-sized wires, the only kind of crimp I have seen is the open-barrel type. You'll find open-barrel crimps on most automotive connectors.

Open-barrel crimps consist of a U-shaped band of metal which is crimped by curling both ears onto the wires.

Splice-terminal-die.JPG (87.48 KiB) Viewed 3688 times

photo from here: http://www.cycleterminal.com/eclipse-tools.html

This one has two open-barrel crimps. One strain relief crimp on the insulation, and one crimp for the actual conductor.

battery-ring-crimp.jpg (52.71 KiB) Viewed 3688 times

photo from here: https://www.easternbeaver.com/Main/Elec ... tools.html

The crimps work the same, as long as you follow the total cross-sectional area rating (typically in CMA).

Splice-crimp.JPG (35.11 KiB) Viewed 3688 times

photo from here: http://www.cycleterminal.com/eclipse-tools.html

You can buy open barrel splices from Digi-Key. They can come loose, or in a continuous reel format:

Crimp.jpg (6.65 KiB) Viewed 3688 times

You'll want to get an assortment to cover a range of cross-sectional area needs.

I buy automotive connectors from Mouser.

An open barrel is... open... so insulating an open barrel splice is a DIY affair with heatshrink tube.

A repair job where I learned the ropes on open-barrel splices, on my Ford Ranger of course. I didn't want to submit my Fiero to my incompetence, not without practice on the test bed.

IMG_3192.JPG (204.08 KiB) Viewed 3688 times

Liquid electrical tape. More for Y-splices, where the heat shrink cannot seal the gap between two adjacent wires.

IMG_3193.JPG (158.02 KiB) Viewed 3688 times

the Permatex product can be found here: https://realfierotech.com/viewtopic.php ... 40#p159404

Self-adhesive heat shrink tube. Note the staggered splices, to prevent a huge lump in one spot.

IMG_3194.JPG (162.11 KiB) Viewed 3688 times

Parts-store splices are more like round tubes, which are squeezed from the outside to squish the wires. These I find do not grip the wires tightly; sometimes the wire can be pulled out of the splice. With the open-barrel crimp, you'll typically break the wires before they pull out.

I also prefer open-barrel splices because they are compact, so they minimize the bulk that is added to the harness.

The crimping tool for an open-barrel splice is pretty universal, which is a plus. The same basic crimping dies will work for a variety of brands of crimps/terminals. I did get dedicated Weatherpack/Metripack dies since those are common on the Fiero.

Soldering in a harness is not generally recommended, since it creates a hard spot that doesn't flex easily. The discontinuity provides a nice place for the wire to break.

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I don't know about the difference in water infiltration between dry and adhesive-lined shrink tube. I have noticed sometimes that dry shrink tube can slide lengthwise on the wire, whereas adhesive-lined won't slide. If sliding can occur, then I assume it's because of a minor gap.

A few years ago I made a conductivity meter. It had stainless steel electrodes, submerged in about one foot of water. The electrodes were press-fitted into 1/4" PVC plastic pipe. After a few days, water had infiltrated past the press-fit (about 3/8" long), and flooded the pipes with water. Some potting resin poured above the press-fit interface made that joint watertight.

If I want something watertight, I assume it needs some sort of sealing stuff, and I don't think too much of it. I haven't dealt with a situation that was so cost-sensitive to start questioning the need for sealing stuff.

[The Dark Side of Will]

In dealing with building The Mule's engine bay harness, I've come across some rules that would be a good addition to this thread.

Anything in the engine bay needs to be rated to 125C. Full stop.
Anything in the interior needs to be rated to 85C.
Raychem DR-25 is *IT* for engine bay rated shrink tube for harness dressing. Raychem describes it as "crosslinked elastomer", but I've also seen it described as "fluoroelastomer". Viton is also "fluoroelastomer rubber". I'm not sure if DR-25 is viton shrink tube or what. It complies with AMS-DTL-23053/16.

[Series8217]

This thread is not really necessary because this page exists: https://www.rbracing-rsr.com/wiring_ecu.html

[Series8217]

Anything in the engine bay needs to be rated to 125C. Full stop.
Anything in the interior needs to be rated to 85C.

Assuming you are talking about wire insulation rating... With appropriately sized conductors, that will generally be sufficient.

To calculate the required insulation rating you need to know the ambient temperature AND the temperature rise of the conductor. For example an 18 AWG insulated wire in free air (not bundled with other wires!) carrying 5 amps will rise in temperature by 10*C above ambient. If ambient is 125*C, now you need at least 135*C insulation rating or the wire insulation will fail. The copper doesn't care... it's the insulation that melts.

Good reference material here on how to size wires: http://www.aeroelectric.com/articles/wiresize.pdf

We generally don't care much about voltage drop in automotive unless it's a sensor signal or non-regulated illumination.

[The Dark Side of Will]

Assuming you are talking about wire insulation rating... With appropriately sized conductors, that will generally be sufficient.

To calculate the required insulation rating you need to know the ambient temperature AND the temperature rise of the conductor. For example an 18 AWG insulated wire in free air (not bundled with other wires!) carrying 5 amps will rise in temperature by 10*C above ambient. If ambient is 125*C, now you need at least 135*C insulation rating or the wire insulation will fail. The copper doesn't care... it's the insulation that melts.

Good reference material here on how to size wires: http://www.aeroelectric.com/articles/wiresize.pdf

We generally don't care much about voltage drop in automotive unless it's a sensor signal or non-regulated illumination.

I was referring more to shrink tube, harness clamps, connector bodies, rubber seals and all the ancillary stuff.
Actually designing for specific current loads is the next step, but requires measuring current loads... and then you can get into fuse stress from motor start-up transients... it's a very deep rabbit hole.

[The Dark Side of Will]

This thread is not really necessary because this page exists: https://www.rbracing-rsr.com/wiring_ecu.html

Yeah, but we have some knowledge on this forum and can discuss

[draven]

In lieu of this discussion...

With my LF3/4 install, I'll be running the LF4 wiring ECU and engine fuse/relay center in the trunk cavity where the 88 GT no longer has the auxiliary engine bay fan passing the engine to fuse/relay/ECU wiring through the rear firewall... however, I still have a mass of wiring to send back up to the front of the car (hi and low can bus and various other signals, i.e. about 40 20-24awg wires)

I'm contemplating running them through the upper rear frame rail for about 1.5' up to the battery location (which is being front mounted) before routing them back into the cabin between the seats.

I know running wiring through frame rails is not recommended, and not necessarily a best practice, however I've spoken to a few experienced restorers and when they do it they utilize a piece of rubber coolant tubing for the length and shove it into the frame rail for harness protection. They even go further, when possible, and mount insulation rings cut out of hard foam to partially suspend the harness in the tube.

Thoughts...

[pmbrunelle]

Actually designing for specific current loads is the next step, but requires measuring current loads... and then you can get into fuse stress from motor start-up transients... it's a very deep rabbit hole.

You can just start with a smaller fuse, and increase size until there is no more nuisance blowing. Of course, the wire needs to be sized for the largest fuse you think you may need.

So, in a DIY project, you are likely to end up with overdesign, but that's OK.

In lieu of this discussion...

With my LF3/4 install, I'll be running the LF4 wiring ECU and engine fuse/relay center in the trunk cavity where the 88 GT no longer has the auxiliary engine bay fan passing the engine to fuse/relay/ECU wiring through the rear firewall... however, I still have a mass of wiring to send back up to the front of the car (hi and low can bus and various other signals, i.e. about 40 20-24awg wires)

I'm contemplating running them through the upper rear frame rail for about 1.5' up to the battery location (which is being front mounted) before routing them back into the cabin between the seats.

I know running wiring through frame rails is not recommended, and not necessarily a best practice, however I've spoken to a few experienced restorers and when they do it they utilize a piece of rubber coolant tubing for the length and shove it into the frame rail for harness protection. They even go further, when possible, and mount insulation rings cut out of hard foam to partially suspend the harness in the tube.

Thoughts...

I don't really like 24 AWG in a car; I find it a bit flimsy and fragile. I like 22 AWG or bigger... but maybe you don't have much choice given the number of wires you're dealing with.

Functionally, I don't see anything wrong with running wires inside a frame rail in general. In the specific case of the Fiero it might be an area that collects water (upper frame rails do rust).

Production would tear you a new asshole for requesting that they snake a wire harness through a passage, rather than simply placing the harness on the engine. Your proposal would be a huge fail of a design.

If you happen to also wear the production hat, and you're the boss of everything, then do what you want That's the nice side of working on a project car.

[The Dark Side of Will]

In lieu of this discussion...

With my LF3/4 install, I'll be running the LF4 wiring ECU and engine fuse/relay center in the trunk cavity where the 88 GT no longer has the auxiliary engine bay fan passing the engine to fuse/relay/ECU wiring through the rear firewall... however, I still have a mass of wiring to send back up to the front of the car (hi and low can bus and various other signals, i.e. about 40 20-24awg wires)

I'm contemplating running them through the upper rear frame rail for about 1.5' up to the battery location (which is being front mounted) before routing them back into the cabin between the seats.

I know running wiring through frame rails is not recommended, and not necessarily a best practice, however I've spoken to a few experienced restorers and when they do it they utilize a piece of rubber coolant tubing for the length and shove it into the frame rail for harness protection. They even go further, when possible, and mount insulation rings cut out of hard foam to partially suspend the harness in the tube.

Thoughts...

I'm not sure anyone would call a wire tuck "best practices". Personally, I'd run the harness through the hole for the engine bay blower. Also, having the harness go through the upper frame rail means that you can not remove the harness from the vehicle without disassembling it (depinning connectors and removing connector bodies from one end or the other), and you'll have to disconnect everything from the engine in order to drop the engine... which you will have to do at some point.

That said, it's your swap and you can do what you want. What's the right way to do something inadvisable? Good question! I would think that getting some type of rubber hose snaked through the frame rail is a great start. You may also want to use DR-25 on the bundle going through the hose, but I don't think that using hard foam supports/separators is a good idea... how will you make sure they're where you need them? Where *do* you need them? What makes them stay there? Use DR-25 like the rest of the "harness community" and you don't have to ask those questions.