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Mil-Spec Wire Harnesses Explained - Hardwired

Breaking Down The Real Meaning Behind Mil-Spec Wire Harnesses

Ryan Basseri
Jun 24, 2013
Photographer: Rodrez

Being in the performance wiring business for the past eight years, I've pretty much seen and heard it all, from mild-spec, tuck-spec, mild-tuck, full-tuck, and everything in between. In many cases, customers are after the holy grail of wiring harness wizardry: the mil-spec wire harness. The term is thrown around so loosely these days that the meaning behind the name has become less and less relevant. So what exactly is mil-spec? What does it do for you? And most importantly, why would you shell out money to own one? These are all valid questions that you may be asking yourself, and the truth is, like most things automotive-related, it has become somewhat of a trend. The term has become intertwined and directly associated with the clean "tucked" engine bays that you see flooding the Honda community, but it's so much more than that. I want to take a moment to set the record straight and help educate enthusiasts about the mil-spec phenomenon and hopefully shed some light on the subject.

01 mil spec wire harnesses explained 61 pin mil spec connector Photo 2/12   |   Here’s a 61-pin mil-spec connector typically used as the bulkhead for the main engine harness.

In the show car scene, hiding wires and being creative is the standard. Many tuners associate the term mil-spec with the infamous wire tuck. There's no real harm in that, but after reading this, I hope that you'll understand the difference between the two and realize the true benefits of a quality wire harness. If it's a clean tucked engine harness you desire, or maybe a full-blown purpose-built motorsport loom, the mil-spec harness has proven itself to be the perfect solution.

The term mil-spec comes from military quality control standards. Each component that the military uses for things like planes, tanks, radios, and weapons earns a military part number. This alphanumeric combo ensures quality and standardization throughout the industry. The part numbers start with MIL and a number or letter designation. Hell, even the paint on Big Mike's Prelude has a MIL part number since it was obtained from a government work vehicle. Sorry to burst everyone's bubble by making mil-spec sound a little less cool, but these are the facts. So what does this mean for our project cars?

02 mil spec wire harnesses explained 61 pin mil spec deutsch connector Photo 6/12   |   Sheepey’s S2000 using a 61-pin mil-spec Deutsch connector

If you've ever noticed the electrical systems on government planes, automobiles, and even watercraft, you might have noticed a standard. The wire is often Teflon-coated for heat defense as well as fighting RF interference. The wiring technique is often quite complicated with special touches like service loops for strain relief as well as twisting strategies to keep the wires flexible and able to bend in any direction. Special high-quality heat-shrinkable tubing is also used to keep the wires tidy and clean. The single most noticeable and recognized item on the harnesses of these vehicles is the mil-spec bulkhead connector. What is a bulkhead, you may ask? In this case, a bulkhead serves a specific purpose, allowing a pathway for the wires to pass through an object. This object may be an engine's airbox, a firewall, or even a fender well where wires might be. When you really break it down, this stuff seems very basic and very bland, but don't worry, we'll touch on the exciting stuff as well.

Mil-spec bulkhead connectors use a circular design with barrel crimps and high-quality gold terminals to ensure perfect connectivity. These connectors use threaded-on back shells to serve as an anchor for a rubber-sealed boot that acts as a barrier for the elements. High-end motorsports have taken mil-spec a step further, with connectors designed specifically for motorsport use. Deutsch, a company that manufactures mil-spec connectors for military use, has also introduced motorsport-specific connectors under the Autosport brand. These high-quality components offer a built-on back shell to guarantee absolutely no failure. They are also quite a bit lighter and come in smaller wire size options; important when weight savings can give the end user an edge over their competition. These high-quality locking bulkheads offer a quick-disconnect "flip of the wrist" locking and unlocking mechanism, making them super fast and simple for a race team to remove engines and components in a hurry.

09 mil spec wire harnesses explained autosport connector lineup Photo 10/12   |   Just a small sample of Autosport's vast lineup- a variety of different sizing for various automotive uses.

The mil-spec harness has served as a staple for the modern-day Honda enthusiast, and taking your car to this level typically shows others that you mean business, whether it be on the track or on display. The biggest and most significant benefit of the mil-spec harness, in my opinion, is the ability for the harness to be customized to very specific needs. Finding a professional harness builder to make a high-quality setup, custom tailored to your specs makes this process an investment, but one that can serve as the single most helpful mod you can add to your race car or weekend track attacker.

These days, drag Hondas have literally been taken to the next level and beyond with guys like Chris Miller, Tony Palo, Norris Prayoonto, and many others striding into unchartered territory. New standards have been set, records broken, and limits pushed. When serious power is being made, things like poor wiring can be the single most overlooked item in the engine bay. "Noise," or interference, can cause major issues, and when an engine makes big numbers, noise in the wiring can cause critical problems at the track. Proper wiring technique can make or break an electrical system, and twisty tape, ragged solder, and electrical tape are simply not acceptable for high-performance vehicles. Proper-rated wire sizes and solid crimps allow for the "veins" of the engine to function happily.

11 mil spec wire harnesses explained rywire bulkhead mounting plate Photo 11/12   |   Rywire’s bulkhead mounting plate features a recessed cavity to keep the mil-spec harnesses secured, avoiding movement.

Many of my Honda customers are not only after a clean look, but a custom wire loom built exactly to their specifications. As stated earlier, the advancement in technology has grown rapidly, and upgrades like high-end engine control units (ECUs), ignitions systems (coils), and added sensors are more and more common. These engine systems monitor pressures, temperatures, and other vitals to give feedback to the user. Each time a racer breaks an expensive engine, they wish they could have spotted the issue sooner. This is the main reason the successful race teams have converted to high-end management systems like AEM's Infinity, MoTeC, and Haltech. Recording data on how the engine is running and using the information to properly tune the engine is a huge advantage. I've been in situations when looking at data after a recorded session and having noticed red flags like fuel starvation, pressure loss, and temps above normal range has proven beneficial. This info can help sustain an engine, saving the owner thousands of dollars, and potentially keep them in the race. Understanding this, you can see why a properly built system can be so important.

Mil-spec is more than a term, it's more than a tuck-it's a vital tool in the electrical system of a car. Often the most overlooked item, it's given the most important job. Being educated in what it is and how it can work for you is most important before jumping into a complete wiring system. With what we know now, the sky is the limit, and a proper wire harness can make or break a system.

10 mil spec wire harnesses explained autosport female connector Photo 12/12   |   Mil spec Harnesses Explained


Garden Grove, CA 92843
Deutsch Connectors
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