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Multi-wire Splicing

EFI Wiring Fundamentals

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Discussion and questions related to the course Motorsport Wiring Fundamentals

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I was wondering if anyone has had some experience with multi-wire in-line splices (such as the image attached). The source website (https://www.rbracing-rsr.com/wiring_ecu.html) says they used non-insulated step-down butt splices, but don't mention much detail after that.

Is this a recommended practice for wiring harnesses? If so, can someone recommend a product that they have found to work reliably? I am looking to splice 20AWG and 13AWG wires (separately), and it looks considerably tidier than staggered 2-wire splices.

I have also seen Ryan crimp four wires together with an end-splice in the EFI Wiring Harness courses. Does anyone have a recommended product / supplier for the same splice?



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My preferred technique is to strip all of the wires that you will be splicing together and then crimp them together. You can purchase crimps for this purpose in a variety of sizes - In NZ I would try Motorsport Electronics in Auckland. Once crimped then you can simply apply heat shrink over the finished splice. This avoids the need for solder and ensures long term reliability.

If you're concentric twisting a harness and performing these splices at the back of an autosport connector, you can't do them in-line as pictured. In this case I crimp all the wires together in a single bundle with all of the stripped ends collected together, then heat shrink over the splice and while the glue is still soft gently squeeze the heatshrink together with some pliers just beyond the splice. This seals the splice from moisture and ensures it is electrically insulated.

With these sort of splices you will generally be splicing a sensor 0V or 5V for example into multiple wires to go to all the required sensors. In this case you will have a single wire which you could think of as the 5V or 0V 'feed' from the ECU. I will make this quite short (perhaps 40-50 mm) and then crimp the terminal onto it for the autosport connector. Once you've inserted it into the autosport connector you can then bend the splice back on itself so you have all your branches heading down your wiring harness in the right direction and the splice itself ends up hidden behind the heat shrink boot at the back of the autosport connector.

Unfortunately a picture is worth a thousand words and I'm struggling to find one that I've done to post up here :(

good info!

I am struggling to find a source for these multi-wire crimps (see attached screen shot from webinar)

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I haven't been able to find those exact ones either. However, I've found these ones to be just as good (using the same idea of crimping them in a bunch and then folding back the ones I need to continue on):

> I use these for crimping up to 5 20AWG wires: http://nz.rs-online.com/web/p/crimp-butt-splice-terminals/7187665/?searchTerm=718-7665&relevancy-data=636F3D3126696E3D4931384E525353746F636B4E756D6265724D504E266C753D656E266D6D3D6D61746368616C6C26706D3D5E5C647B337D5B5C732D2F255C2E2C5D5C647B332C347D2426706F3D313426736E3D592673743D52535F53544F434B5F4E554D4245522677633D4E4F4E45267573743D3731382D3736363526

> For larger wires (e.g. 13 / 14 AWG) I've been using larger open-barrel crimps that I purchased from a local automotive electrical supply shop (sorry I don't have a link).

For the larger wires, I found that stripping the insulation partway along the cable allowed me to crimp one more wire than would usually fit. I don't know if this is recommended, but it seemed to work fine. I can post a picture later if it will help?

Im not really a fan of those open type of splices. They are bulky, and much harder to get a nice consistent crimp. Especially if you're using a universal open barrel crimper.

I prefer solid parallel splices (pretty much a short butt connector) pic attached, I use size 16-14awg splice and 12-10 splices. Those sizes have served me well, but I do have some 8awg splices handy just in case a nasty 0v splice is just overloaded with sensors. You can crimp these with many types of non-insulated type crimpers. Hex crimpers also work too and leave a cool indent. And with these splices, I can take 3-5 behind a boot and it hardly takes up any space :)

Ofcourse, there are also raychem miniseals, these are pricey (around $1.50 each) and you also need a specific tool DMC GMT232 ($140~ tool)

oh and the splices, in case yall were wondering, are Molex splices. I would post the part number, but part of being a wiring guy is finding your part numbers through catalogs, so I'll let yall do that ;)

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Centrifuge, I tend to buy bags of these connectors (my local supplier Jay Dees sells them for $3~4 for 100) and cut them down to suit.

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