Best way to splice...

I need to splice a 20AWG wire (TXL? or larger from a Holley HP ECU to seven 22759/32-20 wires that lead to the grounds of the engine sensors. What is the best way to do this? I can split 1 into 3, via an inline butt splice, then again split into 3 from 1 (thermister grounds) and then 2 from 1 for the other 2 initial splices. (7 total) This all would happen just prior to 2 deutch connectors (1 for 3 and 1 for 4).

Or... I can do an open barrel splice with all 8 wires in the same splice, either 1 in and 7 out, or all 8 in one side and then a 180 degree bend coming out of the open barrel. All the options would be covered first by SCL then DR-25.

Thanks in advance.

Scott

PS I also will be splitting the 20 AWG Holley power wire into 4 22759/32-20 for the 4 sensors that require 5V power.

I personally always opt for the last option though I'd use a closed Versakrimp parallel splice rather than open barrel.

https://www.prowireusa.com/MLX-SPLICE-KIT

You don't need to buy the whole farm if you know your size - but at least this gives you an idea of sizing options.

Hey Scott,

This is definitely an issue we run into quite a bit.

All of the methods you've described are valid, and electrically there won't be much difference between them. Personally, I try to keep the number of splices to a minimum, so I'd lean towards a single splice with all 8 conductors entering from one side and the ECU wire folded back 180° into the splice.

For eight 20 AWG conductors you're looking at roughly 8,160 CMA, so I'd be looking for a splice sized somewhere around the 10-12 AWG range.

For larger multi-wire splices like this, I generally prefer a closed-barrel splice. I find it does a better job of capturing all the conductors and gives a more consistent crimp around the entire bundle.

Placement is important too. Aim to have the splice located in a section of the harness that will be secured and reasonably rigid, such as in the boot behind a connector or at a junction point. Covering it with SCL or a molded boot also provides some additional strain relief.

The same principle would apply to the 5V supply wiring as well. Sensor power and sensor ground circuits carry very little current, so consolidating them into a single appropriately sized splice is perfectly acceptable.

My preferred way to split single outputs, lets use the 5V reference for example, is to use a bussed Deutsch DT connector (I really wish they made a DTM version for this), and then run all of the 5V reference wires back to a spot near the ECU, into the DT connector.

This provides a few advantages. It is a clean way to splice several circuits, and with the variety of bussed options, you can tailor the connectors to the specific need.

This allows a way to disable the car easily, as a bit of a theft deterrent, if you have the connector(s) somewhat easily accessible, by simply removing the bussed connector.

It provides a trouble shooing point where if you suspect a circuit has an issue, you can pull it easily out of the connector and isolate it from the rest of the circuits, and/or test for continuity on each circuit to the sensor or device it supplies or even to ground, if you suspect a short.

If you find that you need to add more circuits, no need to cut into the harness, just add another circuit pinning it into the connector, and if you run out of room in the existing connector, you can move up to the next pin count connector, or add another bussed connector.

There are other options, like Delphi has what they call "splice savers", that are more comb like, but definitely do the job as well.

That's definitely a valid approach and I can see the appeal, particularly from a future expansion and serviceability standpoint.

Personally though, I try to avoid adding connectors purely to avoid a single splice.

In reality, you're trading one crimped splice for multiple terminals, connector housings, and additional crimp joints. From a reliability standpoint, I'd generally have more confidence in a single well-executed splice than several additional connector terminals. Statistically, you're more likely to have an issue with one of those extra connector pins than a properly crimped splice. A single splice also tends to be cleaner and more compact than adding several larger connectors into the harness.

It also depends on how you implement it. For this particular example, you'd likely end up with a separate distribution connector for the 5V reference and another for the sensor grounds. That means adding two larger DT connectors, whereas my preference is to use a single DTM connector carrying spare sensor inputs, a 5V reference, and a sensor ground. A DTM12 will usually cover this quite well, and depending on how many spare inputs and outputs you have available, you can often include spare outputs in the same connector too. In my opinion, this achieves the same future-proofing and modularity benefits with less bulk, cost, and complexity.

For diagnostics, checking at the faulty sensor connector against a known good sensor connector will usually tell you pretty quickly whether the 5V or sensor ground is missing. From there you can narrow it down to the sensor branch, splice, or connector bus fairly easily.

At the end of the day both methods will work fine. I just tend to lean towards simplicity where possible and save the connectors for where they provide a real benefit.

Would your opinion on this change for a development build?

Meaning a street car that is more of a tinkering project. Evolving constantly.

This shifts the paradigm to one of ease of modification and serviceability.

I noticed the OEM connectors on my car are often a bussed strip inside of an enclosure.

I was looking at the DT bussed connectors as it gives an easy way to add a sensor by adding a pin without having to cut into the harness and re-doing a barrel (open or closed) crimp.

And if I am also adding a mid-harness disconnect (main harness disconnect near the motor/ firewall) would you add a branch point for +12V and sensor grounds for non-shielded connections at that disconnect to lower the number of wires through the disconnect, or carry them all through the disconnect back to a single, central, bussed connector (or barrel crimp) near the ECU?

I understand what you're saying Caleb, but it's never been an issue for me.

If you don't have faith in your crimps, maybe you should solder. :P ;) I jest, we don't need to get into that discussion...

But really, crimps shouldn't be a concern using proper tooling and techniques. The other way to look at it is that if one crimp fails, it will only be that one circuit, assuming it's not the input pin, where as a crimp failure where all outputs are into a single splice likely means the whole system goes down. I guess I just have more faith in my crimps. *shrug* Not to mention there are dozens to hundreds of other crimps throughout the harness, so adding a few to make splicing, serviceability and expansion easier, I think is a good trade off.

The problem with multiple wires into a single splice is that you can get very unbalanced on the in and out, when you need many sensors connected, and even dividing the outs between both ends of a splice, and bending them around, or using a large open splice can introduce more failure points IMO, where the middle wires can eventually work their way out, due to heat cycles relaxing the crimp force, though this would take a long time usually, and if it's properly sealed it shouldn't fail, but I have repaired a number of splices done this way.

Yes, this could require up to 3 separate connectors, one for sensor ground, one for 5V reference, and one for 12V feeds. If there are only a few splices of each needed, then the multi bussed DT connectors that have separate busses all in the same connector could be used. The 12 pin DT bussed connectors can be found in all pins bussed together, 2 6 pin busses, 3 4 pin busses or 4 3 pin busses, other pin count bussed DT connectors can be found in multiple configurations as well. The reality though is that this doesn't add that much volume to the harness, and with careful planning can place them in accessible locations, again to add, or troubleshoot with.

I've tried many different ways to splice, and this is by far my favorite way for sensor grounds, 5V reference and 12V control (ignition feed, boost control solenoid, among other low current 12V feeds). I don't ALWAYS use the bussed DT connectors, some projects just wouldn't benefit from them, but for the ones that I do, I often end up adding more circuits later, which has made doing so much easier.

Here is a picture of one harness I made with this and in this particular case, was very good because I had to add more circuits later. These did get tied to the harness once it was installed in the car.

I also often use DTM connectors to add pull up/down resistors, partly to be able to change the resistance if needed, but also another test point, and just gives a great support for the resistor itself in the end of the DTM connector, especially once potted.

Haha yes, let's not get into the solder vs crimp debate, the internet has had enough of that.

As I said, both are definitely valid ways to distribute a circuit, I certainly didn't mean to belittle your method at all. It's one of those areas where there are multiple good solutions as long as they're executed correctly.

I actually use your approach for pull-up/down resistors and CAN terminating resistors all the time. I definitely prefer adding a connector with a resistor installed rather than permanently integrating it into the harness. It makes changes and troubleshooting much easier.

If Deutsch were to bring out a DTM series bussed connector, I'd probably be a lot more inclined to use that method for sensor power and grounds as well.

Keep up the awesome work and thanks for sharing the examples.