Hey guys! I'm going to be building a motorsports spec wiring harness for my 2G (with evo ECU), and I thought it would be nice to document the process for those of you that were curious or had questions. You may have seen this type of work referred to as "Mil-spec", but that is actually inaccurate, as motorsports harnesses are generally constructed to much more strict standards than military wiring. I'll be concentrically twisting this harness.

I'll be using a Link G4+ plug in ECU for an Evo IIIV. This has extra inputs and outputs for various components I'll be using. I'll eventually add this info to my build thread (which I haven't started yet) in a more straight forward form.

My first step was buying new ECU connectors and pins. I simply ordered them from Mouser.com after looking them up from the ECU connector wiki page (which needs some updating). I'm not sure why they're different colors, probably because I missed part of the part number that specifies them being yellow. Oh well, I don't care.





You can see the difference in the 18-22 awg pins and the 16-20 awg pins here. Only the A and D connectors use the 16-20awg pins.





All of the M22759 wire and Raychem DR-25 sheathing will get here today and I'll post an update later about how I determine what gauge wiring to use and how I build splices for branches of power and ground.

Components that will be included in the engine wiring side of things:

Four injectors
Four ignition coils
2GB cam angle sensor
Kiggly crank angle sensor
Intake air temp
Coolant temp (gauge cluster too)
Fuel pressure
Oil pressure
Coolant pressure
Back pressure (EMAP)
Flex fuel
Boost control solenoid
Fan trigger
Fuel pump trigger
Knock sensor
Turbo speed sensor
Bosch motorsports 68mm e-throttle
Can wideband
Tach output
Clutch Switch input
Speed sensor
Alternator
Star-earth grounding for all components

I think that's it but I'll update it if there are additional. Let me know if you have any questions!

Nice this should be awesome! Thanks for doing this!

Very very cool. I'll be watching this.

Subscribe.

Hope you add parts numbers for pin, connectors, heat shrink and such, so we know what to look for when it comes the time to build on.

Thanks to share the process.

MindBlowin03 said:

Very very cool. I'll be watching this.

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miguelmcv said:

Subscribe.

Hope you add parts numbers for pin, connectors, heat shrink and such, so we know what to look for when it comes the time to build on.

Thanks to share the process.

Click to expand...

Thanks guys. I'll post up a full build list once I'm done with the harness itself so it's nice and concise.

Alright, I'm going to try and not make this thread into just a giant wall of text, but there's definitely some explaining to do when it comes to the construction of a harness like this. Probably the biggest thing is that you need to know exactly how many wires you're going to be running as each layer of the concentric twist can only be made up of so many wires.

The first thing I do is sit down and list out all of the components that will be in the particular harness I'm building. Then I figure out how many amps they draw and what size wire I'll need to use from there. I use the wire barn wire size calculator here: https://www.wirebarn.com/Wire-Calculator-_ep_41.html . I size the wires for 5% drop as that's generally acceptable in the automotive world. Here's what my list looks like for the 2G.



Then I go digging through OEM wiring charts and pinouts so I make sure I have the correct ECU pinout and I know how the ECU wants it's power and grounds. A couple notes here helps to keep things organized.



Obviously these are the not-so glamorous parts of the harness build, and what takes up a lot of the time.

Now that we have components and wire sizes calculated, we need to see how many layers we're going to need to run. I use this chart to see what format I need to run to get the right number of wires. If I can't get exactly the number needed, then I'll run a format with a few extra (known as filler wires).



I have sixty-six conductors in my engine harness, which means I'll have to use a two-wire core and end up with 70 wires total. Four filler wires are no big deal.

Now we have to figure out how we're going to distribute power and ground. Since I'll be using GTR ignition coils, I've decided to give them their own relay, as they can draw up to 12amps a piece and I don't want to run all that current through the ecu relay. I'll also be running a Bosch motorsports 68mm throttle body. This means I'll have an ECU relay, an e-throttle relay, and an ignition relay.

Now we can crimp all of our 12v power wires together near the ecu with an open barrel crimp and seal with Raychem SCL, we can use a barrel crimp sealed with the same, or we can use a bussed Deutsch DT connector. I'm undecided at the moment so we'll move on.
We can do the same thing with our 5v power and our grounds.

Another thing to note is that the entire car will be wired with "star-earth grounding" theory. This means that technically the car won't have a chassis ground anymore. The engine block and the battery negative post will be the only spots things will be grounded to (well most likely an isolated battery negative stud located somewhere in the cabin as well as the battery will be in the rear). Now you might think this would create a lot of extra wiring, but it's really marginal, and is a massive help with diagnostics down the road.

I got most of my supplies in. I now just need to sort out a proper firewall connector and we can move on to actual construction!

This is cool.

Awesome write up. A lot of patience

I'm looking forward to learning some new tricks. Thanks for sharing!

As I plan on doing something similar in the future, definitely following this.

Hey guys, sorry for the lack of progress on this. My oem harness was so cut and spliced with different extensions and such that I don't think it would have made a good metric for the measurement of length requirements and such. I think I'll need a longblock in the car to get the proper routing arrangements down, so this may be on hold for a few weeks. I'll be doing some of the battery relocation work next though, which will be to the same kind of standard.

Definitely subscribing to this! Looks like it will turn out to be something awesome, keep up the work!

Definitely following would love to see finished product with you a half a hour away.

Any updates?

Subscribed. Thanks for sharing. The information, processes, & techniques are a tutorial, should be made into a tech article.

Hopefully there are more updates to come!