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Motorsport Wiring Looms


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#1 Curley

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Posted 09 October 2019 - 09:01 PM

During the planning phase of my current build I sough costings for a professional 'motorsport' wiring harness, and, well, they were a lot. Don't get me wrong, having been to a couple of the guys workshops and seen the process I'm 100% comfortable its a fair price but the costs are more than I can spend.

 

Necessity means I'm taking on the task of learning to do the job myself. Fortunately I've been using solid pin style Deutsch connectors for a while so not a complete noob. Tefzel cable is not that expensive assuming the use of a single colour insulator. One area I'm not 100% on is do I really need to bother with concentric twisting the loom?

 

I mean, every production car I've ever worked on has a loom made of straight run wires bundled together in some sort of containment/protection. Therefore, to my mind, concentric twisting is one of those theoretical diminishing returns type concerns. Technically true but not 100% necessary?

 

I assume therefore that as long as no one wire is under any undue stress & that the loom is supported along its length it would be ok to go with a simpler construction method & lace the loose bundle before heatshrink?

 

Do any of you guys with hours on their race cars have a strong opinion on this topic? Have you ever had a DNF as a result of unreliable electrics and if so what did you do to fix it & what would you do differently if you did it over?


Edited by Curley, 11 October 2019 - 06:33 PM.


#2 nicklouse

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Posted 09 October 2019 - 09:17 PM

Ah Motorsport harnesses.

 

what type?

 

full car for a rally car? Or just the basics for a hillclimb car?

 

on a Hillclimb car as you have so few electrical parts it is not really worth it. All power supply wires are fused and have a led to show when which fuse has failed.

 

signal wires are on their own sleeved with what they need. 2 core or 3 core or 4 core (or a pair of 2 core) makes them easy to replace between runs if something fails.

 

my wires are all bigger than needed that is to say not the minimum requirement.

 

now you could go to multi pin bulkhead connectors etc see latest Binky. 
 

but think on what if a wire needs replacing for you to keep on running.

 

when we did the endurance cars 924 and 944 we did not do anything special to the harnesses.



#3 Curley

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Posted 09 October 2019 - 10:28 PM

Circuit racing but must be road legal. Control systems are free. Yes to bulkheads (or just bulky)

leZFAfo.jpg

On my last car I used W23 circuit breakers in place of fuses and made one working loom from 2 factory looms. It worked well & having the breaker instead of fuses was a real plus as it made fault finding easier.  My only real complaints were the weight and the amount of time it took to do, I reckoned I'd have been quicker to make one from scratch.

 

Something that all of the pro looms specified was Tefzel M22759/32 as it cut weight. They all also specified DR-25 heat shrink and were all fully sealed. 

 

I figured on attempting something of a Clubman level harness that takes the best parts of a real motorsport harness but without the cost of the alloy motorsport connectors. Let's face it, it's a mini not an F1 car. lol

 

I too have planned on using a larger gauge than needed. Mostly 16 and 20awg, some 22 for sensors. I'm not going to bother with 18 or 24. DR-25 in exposed areas such as the engine bay & around fuel, expandable braid in the cabin, solid pin DT/DTM/DRB connectors, fully sealed boots on the connectors & supported every 10-12".

Edited by Curley, 11 October 2019 - 06:34 PM.


#4 nicklouse

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Posted 09 October 2019 - 10:43 PM

I would support at 8” the same as we do for braided brake hose. Then if you run them together it matches.


Edited by nicklouse, 11 October 2019 - 06:36 PM.


#5 Curley

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Posted 11 October 2019 - 06:35 PM

Good point thank you. 8"it is :-)


Edited by Curley, 11 October 2019 - 06:36 PM.


#6 Avtovaz

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Posted 13 October 2019 - 07:58 PM

"i think" the twisting is to reduce the size of the loom for when they add the covering.

 

I ve just made a loom for my bmw engine bay, its got a b230 engine in it now and uses microsquirt. Points ive picked up on are to use crimps and no solder, support it as said  every 8" or so. I went with the telsa cloth tape on it, i think heat shrink can hold water. Although, if you get some clear heat shrink, you can make little lables for the plugs and heat shrink it on. Ive gone for super seal connectors too, and use the proper tool!



#7 Curley

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Posted 13 October 2019 - 08:10 PM

Thanks. As i understand it concentric twisting is intended to make the loom more flexible while also ensuring all the wires are under equal tension. 



#8 Kaj

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Posted 15 October 2019 - 09:14 PM

I've worked in aerospace all my career and aircraft loom are all made straight but are combed to make them neat and suit the t-offs. If you use DR25 type heatshrink there is no going back when all shrunk down. What I did for my engine wiring was to use heatshrink sleeving as a wrap, by cutting down it and then wrap the loom as a tape. Secure the ends with a cable tie to hold in place. This gives more maintainability and is pretty robust and looks ok.
You can purchase heat shrink in rolls from Toolstation which is much chea per than pukka DR25.
Hope this helps.

#9 MGMiniman

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Posted 16 October 2019 - 03:45 PM

Use the loom tape available from most Auto electrical suppliers like 12Volt planet.
The stuff that has no adhesive and is flexible. Spiral wound so that it will flex on installation.
Just anchor the ends with adhesive tape.
If you use and adhesive type tape it will not flex and will go sticky in a very short time.
It’s also very cheap.

#10 KRM_Simon

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Posted 19 October 2019 - 05:44 AM

Hi Curley,

On my previous rally car I didn't do a full loom but did several part looms for adding various ancillaries - all done concentric twisted, self taught and what I will say, when you have done a loom and it has taken you ages (and it will, its hard work, especially with very long wiring runs with various wires t-ing off) you look at it and you'll think, wow that looks pretty smart - almost professional infact, then you'll put heat shrink over it or braiding and you'll never see it again.

This build I'm doing it differently - I'm paying some to do it, someone who does a lot of this sort of thing on some very high end rally cars and these were some of his thoughts: no point concentric twisting, the bundles of wires you are dealing with aren't really big enough to warrant it, the loom will still be fairly flexible and aslong as it is properly supported (he recommends 6") you wont be adding any stress either. not sure on the sleeving he was using but not heatshrink but he mentioned the ability to pull through a new wire if you have a fault on one (another reason not to twist - you'd never manage it). Bulkhead connectors, unecessary for my application (cant remember if you were going removable front or not) they would rarely get disconnected as I'm not going for removeable front end, but instead less bulky straight connectors behind the dash then through the bulkhead on grommets, still want connectors incase you take a front corner off you only need to replace that section without having to do a splice job.

Cant think of anything else at this moment in time.

 

Simon



#11 Curley

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Posted 19 October 2019 - 07:23 PM

I've worked in aerospace all my career and aircraft loom are all made straight but are combed to make them neat and suit the t-offs. If you use DR25 type heatshrink there is no going back when all shrunk down. What I did for my engine wiring was to use heatshrink sleeving as a wrap, by cutting down it and then wrap the loom as a tape. Secure the ends with a cable tie to hold in place. This gives more maintainability and is pretty robust and looks ok.
You can purchase heat shrink in rolls from Toolstation which is much chea per than pukka DR25.
Hope this helps.

 

 

Thanks for the info on aerospace, I've seen pictures of Airbus assembly with the loom all exposed & straight laid. With all the people I've spoken to there are distinct camps of those in favour of full seal vs those in favour of some kind of method to run new wires.

 

 

Hi Curley,

On my previous rally car I didn't do a full loom but did several part looms for adding various ancillaries - all done concentric twisted, self taught and what I will say, when you have done a loom and it has taken you ages (and it will, its hard work, especially with very long wiring runs with various wires t-ing off) you look at it and you'll think, wow that looks pretty smart - almost professional infact, then you'll put heat shrink over it or braiding and you'll never see it again.

This build I'm doing it differently - I'm paying some to do it, someone who does a lot of this sort of thing on some very high end rally cars and these were some of his thoughts: no point concentric twisting, the bundles of wires you are dealing with aren't really big enough to warrant it, the loom will still be fairly flexible and aslong as it is properly supported (he recommends 6") you wont be adding any stress either. not sure on the sleeving he was using but not heatshrink but he mentioned the ability to pull through a new wire if you have a fault on one (another reason not to twist - you'd never manage it). Bulkhead connectors, unecessary for my application (cant remember if you were going removable front or not) they would rarely get disconnected as I'm not going for removeable front end, but instead less bulky straight connectors behind the dash then through the bulkhead on grommets, still want connectors incase you take a front corner off you only need to replace that section without having to do a splice job.

Cant think of anything else at this moment in time.

 

Simon

 

Excellent info there Simon, I'll take your man at his word on the 6" lol. This was the nail on topic of concentric twisting as I'd been leaning towards it being overkill in this situation. One thing I'm not 100% on yet is the to seal or not to seal. I get the point that once it's sealed it can't be serviced. In all my years the only cabling faults (not electrical) have been due to environmental degradation and/or stress. Loose, soldered wires work harden, become brittle and break. Wires exposed to the element wick water etc. The agreement for suggest that a 'properly' sealed loom is immune to both of these.

 

I think I'm going to have my cake and eat it and try to do both. Given the use of bulkheads at the front I'm ok with having to remake the entire engine loom. Shoot, I'm ok with building two! But I'm also comfortable that DR25 in the cabin is overkill. I'll use over braid in the cabin.

 

With all that said I've spent today in the garage working on the rear of the car. I thought TMF might find interest in the process I'm following with my 'Clubman' loom.

 

Using Deutsch connectors one needs to first load a pin into the crimp tool. The correct crimp tools will come in from 4 sides and crush the solid pin onto the wire. We need to make sure there is a small insulation gap between the end of the pin and the wire. Once installed into the connector a service loom is added - just in case - and, because I'm using mostly white cable, coloured ID bands added.

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b0KJEWb.jpg

 

Rinse & Repeat until all the wires are installed. It helps to align the service loops, ensure they all point inwards & some Kapton tape to secure. The Kapton tape also acts as a barrier and keeps the glue off when you seal the boots.

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JM8cUZV.jpg

 

Before adding any heat shrink the cable are bound, or should I say laced, together to hold their shape. This allows the cables to be combed through as Kaj mentions. Only once the bundles are complete could I lay them onto the car and work out the transition. Oh and you need to be thinking ahead and threading your boots and labels on ahead of time. In the last photo I forgot to add one for the 4 pin and had to undo all the lace :(

1geMQj0.jpg

a2Mo7OJ.jpg

 

I've got more to do before I have to decide if I heat shrink or over braid the rest of the rear loom. I'm going to use DR25 for the rear lights as the cables pass in front of the fuel filler but everything under the parcel shelf is open.


Edited by Curley, 19 October 2019 - 08:06 PM.


#12 warning634

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Posted 23 October 2019 - 08:44 AM

Can you point me in the direction of where I could purchase a good kit for these Deutsch connectors and the crimping tool.

 

I'm just looking into replacing my entire loom and fitting one of the Cartek distribution panels.



#13 Curley

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Posted 23 October 2019 - 02:29 PM

I use Mouser or RS as I have a trade account, be warned though the crimp tool HDT-48-00 is like £250.

 

Kits: https://polevolt.co....ment_Boxes.html

 

An excellent product finder: https://laddinc.com/...product-finder/

 

An excellent source of information: https://www.rbracing...wiring_ecu.html

 

The Cartek PDM are good, I looked at them myself, and been using their battery isolators for years.


Edited by Curley, 23 October 2019 - 02:32 PM.





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