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What's inside an LMS-EFI harness? Part 1

The Raychem DR-25 heat shrink and yellow labels just seem to say "RACE CAR", but a quality harness is more than the visual effect.  What is inside the shrink wrap and how it is prepared is really what matters in terms of performance and reliability.

Most kit harnesses begin life with polyetheylene coated automotive spec wire with bare copper strand conductor wire.  As anyone who has torn into a car with auto spec wire underhood can tell you, this wire simply does not stand up to the abuse of underhood conditions very well.  Add in the added heat and stress of high performance applications or all out racing conditions, and a better solution is called for.  Being stranded on the side of the road in your daily is one thing.  But having your race weekend ruined by an otherwise simple electrical gremlin is simply not an option.

Our harnesses begin with mil-spec M22759/32 wire, which holds many benefits over standard auto spec wire.  The individual copper strands of the M22759 are tin coated for corrosion resistance.  We've all seen bare copper wire turn green when exposed to the elements.  This corrosion hurts conductivity, as the majority of electrons flow on the surface of the individual strands of wire.  With tin coated wire, the process of corrosion is greatly mitigated and superior conductivity is ensured in tough environments throughout the wire's life span.

The outer wire coating of M22759/16 is Tefzel, a DuPont trade name, or ETFE.  In short, Tefzel is much tougher than what you would find in the polyethylene coated wire.  It's stronger in terms of abrasion resistance, has a higher heat tolerance, and is more flexible.  Polyethylene is generally rated to about 125C.  While ETFE is rated to 150C and can withstand periods of 300C for up to 7 hours.  The tougher coating also allows it to be much thinner while still offering superior abrasion resistance.  This translates into a smaller loom package.  In short, ETFE is a superior wire to what most ECU manufacturers supply with their ECUs and anything you'll likely find in the local auto parts store.

In short, the wire we use is smaller, lighter, stronger, more flexible, offers better corrosion resistance, all while being price competitive with the less capable wire offered by many of the aftermarket ECU manufacturers and by the OEs.  There really is no excuse to use a lesser capable wire as the basis for your project.

In our next post, we'll discuss the technique and benefits of concentric twisting.