Last month we started covering one of the most feared aspects of any automotive project – the wiring. If you missed Part 1, you can check it out here. Wiring is a pretty broad topic and there was no way I could do justice to the topic in one article. Actually, I’m going to struggle to do so in two, but hopefully these articles will offer some useful pointers and take some of the fear out of your next wiring job.
This month we’re going to look at a few more aspects such as shielding inputs, the importance of grounding, and protecting your wiring harness.
Staying Grounded
If I had to come up with the one single problem that I’ve repeatedly seen the most trouble from when it comes to wiring, it’s poor grounding. Everything the ECU does is dependent on the accuracy of the voltage input it sees from all its sensors and if the voltage the ECU receives fluctuates then it can cause all sorts of nasty problems.
When we talk about voltage, most people don’t consider that the voltage measured is always relative to something called ground or zero volts (also often called earth). It’s crucial that the ground reference throughout the entire car is consistent, and this involves properly grounding the ECU to the engine block, the engine block to the chassis, and the battery to the chassis. A common trap here is when reassembling a car after painting. It’s critical to scrape the paint away underneath any earth straps to ensure they make proper contact with the chassis. Paint is a very poor conductor.
If you suspect your car has a grounding issue, a good test is to use a multimeter on the ohms setting to measure the resistance from the engine block to the battery negative, chassis, and ECU power grounds. If everything is grounded properly you should be seeing less than 1 ohm of resistance. If you’ve got more than this then it’s time to check the condition of your earth straps and your ground wiring.
Eliminating Interference
The engine bay is an electrically noisy place and this can be a huge problem when the ECU needs to receive clean signals in order to do its job properly. When I use the term ‘noise’, I’m talking about EMI or electromagnetic interference, and while there are many sources of EMI, the engine’s own ignition system is often a culprit.
The most critical inputs that all of the ECUs calculations are based on are those that tell it what the engine RPM is and which cylinder is firing (collectively these inputs are often referred to as trigger inputs). If the ECU is receiving noise on these inputs it can cause all sorts of issues including misfires and poor running.
To help reduce the chance of EMI effecting the signals to the ECU it’s essential to use shielded cable for these important trigger inputs. A shielded cable includes twisted conductor wires that are connected to the sensor and a shield that surrounds the conductors. The shield acts by picking up the electromagnetic interference and conducting it through the shield to ground, preventing the interference reaching the conductors.
When using a shielded cable it’s important to make sure that the shield is properly grounded at the ECU. This is referred to as a shield drain as it harmlessly drains any EMI to ground. It is, however, important to drain your shielded cable to the correct place on your ECU. The ECU wiring diagram will have dedicated terminals for this job.
Where Does That Wire Go?
For a wiring harness to do its job properly it’s pretty obvious that every connector needs to be plugged in to the correct spot, right? While it might be obvious, when we’re dealing with a complex harness with many similar connectors, sometimes mistakes can happen and that’s why it’s so important to label your harness. But how?
In a proper mil-spec harness you’ll usually see small yellow or white labels with the connector name printed on them, but have you ever wondered how this is done? These labels are actually printed onto a roll of heat shrink tube using a thermal printer. The printer prints your labels and then you simply cut them to length, install them and then shrink them down on your harness. As delivered, these labels aren’t very robust though, so they are normally covered with a length of clear heat shrink.
Just a few years ago these label printers were pretty expensive and hard to justify for a home enthusiast, but these days basic models can be purchased for as little as US$150. For a one-off project, many of the wiring suppliers or harness builders will also print off labels for you – for a cost, of course.
It’s A Wrap
Protecting your wiring harness is almost as important if you want it to last. A car is a harsh environment to keep your harness alive – there’s intense heat, corrosive chemicals and abrasion to consider just to name a few. At the pointy end of the spectrum, Raychem DR25 is the choice of most professional harness constructors. This is a heat shrink tube that offers an attractive and reliable way of covering your harness, and it’s resistant to most of the nasties that the automotive environment has to offer.
DR25 can be difficult to use over a harness that isn’t concentrically twisted though. It has a shrink ratio of 2:1, meaning that once recovered after heat shrinking it is half its original diameter. This can make it hard to get over a harness that isn’t concentrically twisted, and in this situation once shrunk down it can also reduce the flexibility of the harness.
A couple of steps down from DR25 is the fabric braided weave that’s quite common in many entry-level harnesses. This is a much easier product to install over a harness that hasn’t been concentrically twisted and it also tends to maintain good flexibility in the loom as it isn’t shrunk onto the wires like DR25. Fabric braided weave, however, needs to be secured at each end using a heat shrink tube to prevent it becoming frayed, and care is needed when installing this as the melting point of the fabric braid is quite low.
But Wait, There’s More
These two articles are really just a small example of what goes in to producing a reliable wiring harness. There’s a lot more to it that I simply can’t do justice to in this space, but hopefully you’ve picked up some tips and some new information that you can apply to your next project. I guess more than anything I want to show that wiring doesn’t need to be scary, and that producing a quality harness is well within the scope of most home enthusiasts provided you’re careful and can show good attention to detail.
If you’ve got this far then you’re probably the type of person with a bit of a thirst for knowledge when it comes to absorbing all you can about automotive performance. While it might not specifically be about wiring, we have a series of free lessons that you can sign up for that will be delivered directly to your email inbox. I consider them to be the minimum amount of knowledge any automotive enthusiast should have on the subject. If you’re interested in receiving these, sign-up here and start learning.
As usual, if you have more questions, ask them in the comments section below and I’ll do my best to answer them there.
Andre Simon
Instagram: hpa101
Website: www.learntotune.com
Photos by Ben Silcock
OFFICIAL SPEEDHUNTERS SUPPLIERS
Dope
Excellent info as always but I would never trust an Ohms reading on a live or ground cable, Volt drop testing is far more reliable indicator of the health of a cable than ohms as only a few strands of cable need remain intact to give a good resistance reading which would not be good enough to work.
Connect the meter wires as per ohms but set the meter to volts, operate the device at the end of the cable and look to see anything more than nominal voltage is registered by the meter. only thing over a volt or 2 would indicate a problem
I'm really happy to see well-written technical how-to articles in the mix here on SH. Please keep them coming!
another tech article that doesn't make our nose bleed. nice article as usual!
This couldn't have come at a better time, I'm just about to tackle my first electrical gremlin and this has armed me with more knowledge than I had previous. Nice, to the point and non-mind boggling, cheers again Speedhunters!
Thanks for this article guys. I cucurrently a member of HPA and throughly enjoy the programs made for the academy, wiring especially. These tips and tricks are throughout the lessons and a truly beneficial. I just hope we can one day be taught the concentric twist!
-Kyle
Getting ready to go through the harness for my EG33 swap so this comes at the perfect time!
VW made the coil pack plugs on my 1.8T out of crap plastic and I've already had to replace them once, so I wanted to add in a single plug down the line a bit, so I could unplug just it and remove all four coils together. Since those are shielded wires (which I didn't know the purpose of until now), is there any special measures I need to take to keep them shielded? Or should I just leave it alone? Thanks!
Another guy did what I want to do, but he didn't respond to my questions about it.
I think having a solid ground on the alternator is a honorable mention as well. I didn't have adequate ground on my new alternator after we swapped the engine in my project car. The car wouldn't hold a charge for more than 30 miles, should have been obvious but it didn't get figured out for months.
This series of articles keeps costing me money. $500 in pieces to rebuild the harness in my race car. Now $100 for that slick label printer. But hey, I just can't resist.
I would like to someday create a custom harness for my vehicle. Could you possibly give us some links to reputable companies that sell supplies and tools needed to create one? Thank you for the articles, HPA is an awesome resource and it's cool to see some knowledge trickling in on Speedhunters. Aloha!
@Doug Ohm my god. sick pun.
Kyle Akre There's a quick summary of it in Part 1 of the Wiring series.
http://www.speedhunters.com/2015/09/knowledge-boost-tackling-your-wiring-nightmare-part-1/
This is easily my favorite series Speedhunters has ever posted. I have experience in this with Aircraft grade wiring harnesses from my experience in the military. The T.O. for Cannon Plugs is about 6" thick. Finding exactly the right connector, strain relief, and pin type is an art form. You've just added a new item to my list of things to buy. I didn't know they made a portable heat shrink labeler.
Keep up the great work!
@DanielWGK glad you're enjoying the articles! Just to be clear, the label printer we are using in the picture is a little more than $150 USD however cheaper entry level models can be purchased that will still do a great job.
Alika80 you can try these companies for wiring consumables:
http://www.prowireusa.com
http://www.milspecwiring.com
http://www.rywire.com
http://www.racespeconline.com
@Doug just to be clear, the label printer we're using is a touch more than $150 USD but search amazon and you'll find well priced entry level models. Sorry to keep you broke
earmenau Typically the alternator in my experience is well grounded through the alternator body to the engine so I've seldom seen the need to independently ground it. Of course if your engine isn't grounded properly then that will be an issue. It's also important that the voltage sense and the main power feed from the alternator are properly connected.
ChristopherAnderson1 it's not uncommon when modifying factory coils for motorsport use to pot the wires directly into the coil and then terminate them in an autosport connector. The downside though is it becomes impossible to replace just a single coil.
If you're using shielded wires you can connect the shields together in a single drain and pass this through the autosport connector (or a DT/DTM is totally acceptable). The wires on both sides of the autosport connector need to be shielded too.
BrandonCurry Happy to help
Kyle Akre thanks for the kind words! We are aiming to have a higher level wiring course available at some point which will cover concentric twisting. Right now I can't promise when that will be unfortunately.
Steve Hayward we're not planning on stopping so you're in luck
@Richard valid point mate. We're a little space limited with these articles so it's not always possible to go into as much detail as the subject requires.
Andre Simon I immediately looked them up. I'd end up with the lowest cost 3M unit that does heat shrink. My experience with heat shrink printers is all with Zebra branded units. We always had problems with jamming.
I've got a 2.3-16 project coming up that is going to need a full wiring harness. We'll see how it goes.
Andre Simon And now that I look into it, I've mixed up brands with another brand. The heat shrink printer we had jammed but I don't remember the brand.
Andre Simon ChristopherAnderson1 Thanks for the reply! I was actually planning to keep the OE connectors on each plug, but since I'd almost never use them, they'd be far less likely to break. I think the image above is a DTM connector, so I was going to do that, so I'm glad you agree. Thanks again.
Thank you sir! I have to get signed up on HPA. I'm a service technician by trade and always looking to learn new things. Harness building is on the list. Aloha!
Andre Simon Kyle Akre Oh Yes, i have seen your plans, and cant even being to explain how much i want to see that! While practicing is something i have to plan on doing, seeing a pro do it, and offering any time saving tips and tricks are truly worth their weight in gold!! Again, cant wait to see whats in store!
Thanks again for providing this info. For OCD guys like me, and people who hate doing things twice (if avoidable) these courses are exactly what i was looking for!
-Kyle
This is more of an umbrella comment on all Knowledge Boost articles, but I really appreciate what you're doing Andre. Every article has a wealth of information that is helping us Hunters well informed on our present and future projects, and even when we haven't arrived at obstacles touched upon in an entry, it gives us plenty of foresight and a sense of familiarity when we begin to tackle those areas.
Always glad to see Knowledge Boost in the title!
And always have some WAGO quick connectors in yout pocket. They come in handy if you have to testfit something because its possible to remove them without tools or cutting wires.
http://global.wago.com/en/products/product-catalog/terminal-blocks-connectors/installation-connectors/compact-splicing-connectors-all-conductor-types-221-series/index.jsp
IRONWOLF RD Love this feedback!
IRONWOLF RD thanks for your kind words! It's a complex world out there and hopefully these articles will help speedhunters everywhere to understand just a little more about what's going on
Sputnik1337 thanks for the tip, that's not a connector I've ever used before - I had to google it
Smart design for a quick test fit but I wouldn't be relying on them longterm for anything mission critical.
@Richard To complete the picture for the readers, a resistance reading (Ohms) doesn't tell the entire story of how good of a connection you have; voltage drop on a cable is dependent on amount of current and the resistance (research Ohm's Law for more details). A resistance reading with a multimeter uses extremely low current, so can fool you into assuming that an insufficient connection is actually sufficient. Once the actual working current is applied, things can suddenly appear very different.
Hey this may be completely unrelated but what kind of multimeter would you recommend for an absolute noob? What kind of specs should I be looking for? I've signed up to the mailing list and look forward to these articles, but forgive me, I haven't dedicated much time to learning about wiring. I will eventually get round to my first wiring project though which would be installing a GPS tracking device or kill switch!
John Key NZ a Digital AC/DC Multimeter can be had for as little as £7 / $16 and will do everything that a $50 does, not much different, I'm a software engineer who works with embedded devices and use a £15 meter for everything from 400v embedded LED Matrix to my car
John Key NZ you don't need to be spending much money for a basic multimeter, and pretty much any meter will handle the basic functions you will need. The SP Tools meter we used in the article is entry level and very cheap. You'll be able to pick up something suitable from Jaycar, Dick Smiths or Repco for around the $50 NZD mark
Did you forget to mention Raychem HFT5000 woven heatshrink? This stuff is great and easy to use also!
Wow, since reading theae wiring articles, i've grown more Cojomes to tackle my 1uz rx81 swap. Thanms SH amd HPA.
Saver Tip - Walmart have Brother Label Printers for sale for $30
Great articles. Just wondering on the twisted wiring when pulling wires out of the harness are you heat shrinking the harness in sections or pulling the wires through openings in the heat shrinK ?
You mentioned chassis as a ground. Do you ever wire a race car with a designated ground running to the battery instead of using the chassis. I have wired a few drag cars this way to allow me to ground to common points and eliminate multiple ground loops and the chances of noise.
John Key NZ I've found that being able to use a K type thermo-probe is super handy especially as bungs and probes are cheap as and the info is useful. Otherwise I agree with the other comments, get what you can and the key is learning how to use it.
Andre Simon Sputnik1337 and mini safety pins! Doesn't make an opening in the insulator like a probe and you can clip and alligator to it rather than holding a pointy probe into the wire
@fabrik8 People that know what they're talking about in internet comments? What's happening to the world lol
the car was very good
really really like to see the car that shiny new car fits like made for walking trailsthe car was very good http://utamadomino.com/app/img/peraturan.html" rel="dofollow" target="_blank">http://utamadomino.com/app/img/peraturan.html and very fast http://utamadomino.com/app/img/jadwal.html" rel="dofollow" target="_blank">http://utamadomino.com/app/img/jadwal.html mix of colors http://utamadomino.com/app/img/promo.html" rel="dofollow" target="_blank">http://utamadomino.com/app/img/promo.html from which to http://utamadomino.com/app/img/panduan.html" rel="dofollow" target="_blank">http://utamadomino.com/app/img/panduan.html make want pobud http://utamadomino.com/ see hatnya http://dokterpoker.org/app/img/peraturan.html" rel="dofollow" target="_blank">http://dokterpoker.org/app/img/peraturan.html kecepatanya http://dokterpoker.org/app/img/jadwal.html" rel="dofollow" target="_blank">http://dokterpoker.org/app/img/jadwal.html was very nice ,http://dokterpoker.org/app/img/promo.html" rel="dofollow" target="_blank">http://dokterpoker.org/app/img/promo.html suitable for a "http://dokterpoker.org/app/img/panduan.html" rel="dofollow" target="_blank">http://dokterpoker.org/app/img/panduan.html sharp bend http://dokterpoker.org or not sharp I guess motorists http://633cash.com/Games like this is http://633cash.com/Pengaturan" very skilled in the speed I hope I can membilinya someday will whether http://633cash.com/Daftar http://633cash.com/Promo there are http://633cash.com/Berita new cars http://633cash.com/Livescore are better I http://raksasapoker.com/app/img/peraturan.html" rel="dofollow" target="_blank">http://raksasapoker.com/app/img/peraturan.html 'll wait for it , with a stylish car classic http://raksasapoker.com/app/img/jadwal.html" rel="dofollow" target="_blank">http://raksasapoker.com/app/img/jadwal.html style I http://raksasapoker.com/app/img/promo.html" rel="dofollow" target="_blank">http://raksasapoker.com/app/img/promo.html also like http://raksasapoker.com/app/img/panduan.html" rel="dofollow" target="_blank">http://raksasapoker.com/app/img/panduan.html to see would be http://raksasapoker.com/ whether there is a http://yakuza4d.com/peraturan" rel="dofollow" target="_blank">http://yakuza4d.com/peraturan car that is http://yakuza4d.com as fast and forius http://yakuza4d.com/home like in the "http://yakuza4d.com/daftar movie , the car very http://yakuza4d.com/cara_main good car http://yakuza4d.com/hasil designed a way apparently hopefully http://yakuza4d.com/buku_mimpi there will be new cars more good and the price is quite pantastis then chances are I can membilinya the same as you have at this time
the car was very good
really really like to see the car that shiny new car fits like made for walking trailsthe car was very good http://utamadomino.com/app/img/peraturan.html" rel="dofollow" target="_blank">http://utamadomino.com/app/img/peraturan.html and very fast http://utamadomino.com/app/img/jadwal.html" rel="dofollow" target="_blank">http://utamadomino.com/app/img/jadwal.html mix of colors http://utamadomino.com/app/img/promo.html" rel="dofollow" target="_blank">http://utamadomino.com/app/img/promo.html from which to http://utamadomino.com/app/img/panduan.html" rel="dofollow" target="_blank">http://utamadomino.com/app/img/panduan.html make want pobud http://utamadomino.com/ see hatnya http://dokterpoker.org/app/img/peraturan.html" rel="dofollow" target="_blank">http://dokterpoker.org/app/img/peraturan.html kecepatanya http://dokterpoker.org/app/img/jadwal.html" rel="dofollow" target="_blank">http://dokterpoker.org/app/img/jadwal.html was very nice ,http://dokterpoker.org/app/img/promo.html" rel="dofollow" target="_blank">http://dokterpoker.org/app/img/promo.html suitable for a "http://dokterpoker.org/app/img/panduan.html" rel="dofollow" target="_blank">http://dokterpoker.org/app/img/panduan.html sharp bend http://dokterpoker.org or not sharp I guess motorists http://633cash.com/Games like this is http://633cash.com/Pengaturan" very skilled in the speed I hope I can membilinya someday will whether http://633cash.com/Daftar http://633cash.com/Promo there are http://633cash.com/Berita new cars http://633cash.com/Livescore are better I http://raksasapoker.com/app/img/peraturan.html" rel="dofollow" target="_blank">http://raksasapoker.com/app/img/peraturan.html 'll wait for it , with a stylish car classic http://raksasapoker.com/app/img/jadwal.html" rel="dofollow" target="_blank">http://raksasapoker.com/app/img/jadwal.html style I http://raksasapoker.com/app/img/promo.html" rel="dofollow" target="_blank">http://raksasapoker.com/app/img/promo.html also like http://raksasapoker.com/app/img/panduan.html" rel="dofollow" target="_blank">http://raksasapoker.com/app/img/panduan.html to see would be http://raksasapoker.com/ whether there is a http://yakuza4d.com/peraturan" rel="dofollow" target="_blank">http://yakuza4d.com/peraturan car that is http://yakuza4d.com as fast and forius http://yakuza4d.com/home like in the "http://yakuza4d.com/daftar movie , the car very http://yakuza4d.com/cara_main good car http://yakuza4d.com/hasil designed a way apparently hopefully http://yakuza4d.com/buku_mimpi there will be new cars more good and the price is quite pantastis then chances are I can membilinya the same as you have at this time
Hi I like to know more about concentric wiring and how to tap off wiring as it is all twisted