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FREE Fueltech Concentric Twist Wiring Reference, Fueltech - The Fairmont

Updated: Feb 1

Concentric Wire Twisting Design Overview

For those seeking a layout/pin-out reference when building their very own Fueltech FT600 concentrically twisted harness, look no further.

With this being the first blog post to test this added website functionality and layout why not keep the "READING" to a minimum and visuals to a maximum.

You will see first-hand how the harness was planned: from wire color, to wire size, the layer each wire was placed in, and even which heat shrink size to use. (Microsoft Excel used to show how it can be done with low-cost planning tools, otherwise there are excellent wire harness planning tools available on the internet, like Rapid Harness, that are extremely powerful but can cost spend several hundred USD/month.)

Disclaimer: use these images as references at your own risk, some notes are not visible without sharing the entire file.

FT600 Connector A: The Outputs

*If using outputs to trigger relays or other devices under 5amps, consider using 22awg wire size.

FT600 Connector B: The Inputs

*Shading in the spreadsheet highlights twisted pairs (Light Green), source wire for splicing (Light Blue), spliced wires post source splice (yellow-ish), filler wire (violet), and shield grounds from shielded wire (grey).

FT600 Peak and Hold Injector Driver

*If using Peak and Hold Driver(s), we suggest opting to use 22awg wire from FTA to FT Peak and Hold Module for fuel injector signals with filler wire if needed. From the P+H Driver to injectors we use 16-18awg (application dependent).


  • PLANNING IS KING - seriously...a harness such as this will take longer to plan than to build (But hopefully this helped speed that up for you).

  • Use the inside-out method. Do not push terminated wires into connector if they are not part of the current layer you are working on. They will cause a nest and make it challenging to work on.

  • The innermost and outer most layers are laced in the opposite direction of the twist - knotted and taped. (We use kevlar lace and 1/4" kapton tape)

  • Try using as much of the same size wire as possible when braiding, this makes the process much easier to plan (simply add 6 wires next layer out)

  • All cut wire lengths should be 15% LONGER AT MINIMUM than required, we use 25% extra for everything we do and keep all the offcuts for splicing later if needed.

  • Concentric twisting can be done with the unterminated harness or TXL wire, however M22759/32 Tefzel wire is roughly 30% lighter and the thin insulation has a teflon like feel making it easier to work with (less likely to knot as well)

  • DO NOT PUT FLAGS OR LABELS ON YOUR WIRE - Not only will they hinder your progress by being cumbersome, but they can also negatively affect how your wires lay. The adhesive on them can pick up dirt/grime and it can spread to every wire in the bundle. If needed, use wire color or smaller colored heat shrink bands as visual identifiers.

  • ALWAYS Plan on "ohming" the harness at the end (Continuity checking with multimeter...*BEEP BEEEEEEP*). Simply push a DTM/ATM Pin Terminal in the position of interest on the SuperSeal Plug connectors to make testing and probe touching easier.

  • Soap and Isopropyl Alcohol is your friend: clean your hands, workstation, and products before handing any wire or braiding.

  • Each layer will only turn out as nicely as the one underneath it, take your time.

  • When removing zipties cut the HEAD of the it off (The square part) and not the band - you may accidentally cut the insulation by trying to wedge the sharp cutter around the band which can lead to manor headaches and even rebuilding.

Tools/ Materials

  • Service loop Needles: We offer what we found works best for us on the webstore here:

  • Zip Ties: AMAZON, they are a cheat code to extra hands so have alot of small ones on hand (roughly 3k 4" Zips were used for braiding this entire vehicle). The larger ones may push wires around on tightening while smaller ones deform to match the bundle better.

  • Heatgun: There are many options openly available for purchase. We use the shrouded tip for most of the harness as remove for booting (and some confined splices).

  • Wire: Tefzel or TXL, Tefzel preferred. Different wire strippers may be needed if going the Tefzel route: size 20 awg Tefzel is smaller and lighter than size 20 awg TXL. We offer some options here:

  • Connectors: you can source from many places like Fueltech, other major parts stores. We also stock a large variety. (If you are not in the US, send us a message to work on shipping options- we are still updating the website)

  • Wire covering: you will want something flexible after being heated/recovered (one of the benefits of concentric twisting is flexibility). We offer multiple options as-well-as a Mil-Spec alternative to the commonly used Raychem DR-25:

We ask that you please leave a comment about what else you would like to see and subscribe for more useful information and content; we promise not spam you. Our single goal is to provide our customers and community with great information.

Please let us know if you liked this type of content or how you would like us to change it by either sending us a message or leaving a comment at the bottom of the page. Feedback of ALL kinds helps us learn what our customers value so we can invest in providing the most useful content!

Additional Photos of Our Work

Backside of the dash prior to final epoxy and boot recovery:

Transmission Harness (Using black Milspec PI-HSB Heatshrink)

Office Place all wrapped up:

Spare Fueltech I/O's (Bulkhead and Connectors available on webstore)

Backside of Dash Complete

~Jimmy Plimpton: CEO Plimpton Innovations, LLC

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