Professional Mil-Spec Motorsport ECU Wiring Harness Construction

Electrons

Getting electrical signals from point A to point B is pretty standard thing...Put a piece of copper wire between A and B and the job is done. A century of development has left us with increased specialization in wiring, connection devices, and everything in between point A and B. "Mil-Spec" or military specification, has become the buzz-word in motorsport electrical harness construction. Actually motorsport wiring has developed it's own specialized connectors but it's still largely constructed from aerospace components.

Perhaps "Race-Spec" will become the new buzz-word....Probably not with the trillions of dollars spent on drones, F22's and commercial aircraft.

This is not a definitive guide on building wiring harnesses as this could encompass two wheels, four wheels or no wheels. It does give you a perspective on motorsports ecu wiring and provides access to further literature for you to study and make your own decisions. We build ecu wiring harnesses for our production items and for our own racing activities.

Production OEM Automotive Wiring

On one end of the scale there is OEM automotive wiring, like on your new passenger vehicle or truck, wherein costs are paramount and warranties are offered, in some cases, bumper to bumper for 100,000 miles. Pictured above is a production passenger car harness in GXL and TXL wires.

These vehicles and their myriad of up to sixty microprocessors, connectors, sensors, relays, and switches are tested for years on end in extremes of temperature, humidity, vibration, and electrical interference. There are no mil-spec metal shell connectors, no airframe tie wrapping or concentric twisting, and no epoxied or glue-shrunk connections...Only plastic connectors and crosslinked polyethylene GXL and TXL multi-strand copper wiring without any silver, tin or nickel plating. Guess what, they work just fine...amid increasing complexity, for years on end. A typical mid-sized car will have about 45-70 lbs of wiring.

One time we scrapped out a 20 year old Honda Civic and were amazed at how all the wiring was still in perfect shape...Connector seals were still sealed and clean inside and all the grime, water and heat had not caused any failures. Wiring was still flexible and not cracked. OEM specifications and engineering are pretty damn good.

In short, automotive grade wiring and connectors have a pretty good track record. Not glamorous, but in business, economics and bean counters seldom are.

Motorsports Wiring

This has evolved from aircraft and military specifications wherein light weight and reliability are paramount. As motorsports evolved into an increasingly more sophisticated and expensive professional endeavor, specific motorsport connectors have evolved which are even lighter and smaller than their aerospace counterparts. These products don't have to meet oem production testing requirements...They just have to be reliable in a racing environment which is not the same as freezing in Siberia or bouncing down rural roads in your F150 pickup for decades.

Now NASCAR has embraced EFI...McLaren got the contract just like they did in F1. McLaren TAG-400N NASCAR ecu to the right.

Everything than can slow you down is the enemy....weight of the wires, weight of the connectors and any kind of outright failure, or worse, intermittent failure, which is harder to isolate. This is why F1 might be using tiny 30 gauge wire or why the new McLaren MP4-12C went to extremes in specifying hexagonal aluminum wire to save both space and weight.

Mil-spec circular connectors are the norm, full of all sorts of trickery like strain reducing service loops and concentric twisting for flexibility and more compact wiring harnesses. Reliability at 30,000 feet or going airborne at the Nurburgring...it's all the same thing...well, sort of the same thing.

The connector above features concentric (twist) wiring, service (strain relief) loops at the connector, lacing cord and Kynar clear shrink to hold the wires tightly together near the connector. Kapton tape will cover the wires at the connector to protect them from the special adhesive-lined shapes or RBK Adhesive Lined Shrink. With the wires covered by DR-25 and the Connector sealed by the RBK, the harness will be protected from the environment and from abrasion.

Here a Deutsch Autosport connector has its Spec 55 wires wrapped in Kapton tape to prevent the adhesive shrink from grabbing the wires. The tape allows repairs to be made at a later date. Once the adhesive melts it really grabs the connector, the DR-25 wire covering, and anything underneath it.

Low Static Kapton adhesive tape is commonly available in 1/4, 3/8" and 1/2" rolls. The silicone adhesive does not leave any residue. It is amber in color.

Cost No Object

The McLaren F1, or in this case the F1 GTR race variant, is the pinnacle of cost is no object in the search for perfection. Aside from winning the LeMans 24 Hour Race on its first outing, in a "street car" nonetheless, which pissed off the Germans to no end, the F1 McLaren represents perfection in every detail. They cost more now than when they were built and the planned run of 100 units never was achieved. Naturally the F1 has completely environmentally-sealed mil-spec connectors and the highest aircraft specification wiring.

F1 McLaren GTR wiring

Circular connectors, glue shrunk boots, Raychem DR-25 shrunk over concentric wound silver-plated Raychem Spec 55 XLTFE wiring and, of course, the requisite yellow shrink tube labels covered in clear Kynar shrink tubing. McLaren TAG Electronics ECU. The wiring costs more than your new Mercedes.

Circuit Breakers not Fuses

Passenger cars use fuses everywhere whereas, in motorsports, re-settable aviation-style circuit breakers are preferred. Circuit breakers have the advantage of being re-settable which allows you to perhaps just "push it in" and get going until you diagnose the problem. You also don't need to replace a fuse. Harley used to use truck style thermal breakers...your bike would sign off due to some short and a few minutes later it would run again...but you didn't melt your wires.

Tyco W23 and ETA 483 series push to set circuit breakers are a standard aviation item and are available in many amperages. They "pop up" when they trip and you push them down to reset them. If you are using the popular sealed WeatherPack silicone sealed fuse holders you can use Bussmann 227 series circuit breakers that are a drop in replacement, albeit pricey, for the cheaper one time fuses.

Breakers like the Tyco W23 are usually installed in panels that a race car driver can reach and reset. "Reach and reset" doesn't work on motorcycles. Space is also a premium on motorcycles.

Sealing backs of circuit breakers

Raychem SCL heat shrink can be used to seal circuit breakers and other types of switched from the environment. Much niftier than trying to heat shrink a couple of screw terminals. It is a dual-wall adhesive lined shrink tube with a 2.5:1 shrink ratio.

A greater shrink ratio (4:1) can be accomplished by using DSG-Canusa CDR  adhesive-lined semi-rigid shrink tubing.

Wicked Wicking

In case you doubt the need for epoxy or adhesive-lined terminations, the above picture gives graphic evidence of corrosion traveling down the voids between the strands of copper wires. Since we go to the Bonneville Salt Flats two to three times a year for up to a month, and everything gets bathed in salt, properly sealing the electrical connections is a major concern. Year one OK...year two fix one or two things...year three redo everything. Using adhesive-lined or epoxy-based sealing schemes we can keep corrosion out of our wiring harnesses.

OEM harnesses employ silicone seals on thermoplastic connectors to address these issues. Any gap in the harness can provide a path to internal corrosion.

Sealing with Epoxy

Sealing boots and shapes that do not have adhesive melt can be done with specialized two part epoxies. Abrading the inner surface and applying the epoxy to the connector and cable before the heat shrinking operation. Epoxy is not applied to the inside of the heat shrink. Resintech RT125. Here the connector is sealed to the cable using V25 Deray thin wall shrink tube (2:1) and sealed with epoxy.

MIL-W-22759/32-35 and 41-46 or Raychem "Spec 55" Primary Wire

Raychem Spec 55 wire has become the defacto standard for motorsports wiring. "Spec 55" is a trademark of Tyco Electronics. The actual designation is MIL-W-22759/32-35 and 41-44. MIL-W-22759/44 is the normal wire of choice with silver plated copper stands. Silver plated copper (SPC) strands have a higher temperature rating than does Tinned copper (TC) strands.

Spec 55 Single Wall or "interconnect" wire carries the designation 55A011-xx-xx. Spec 55 Dual Wall or "airframe" wire carries the designation 55A081-xx-xx.

"XLETFE" insulation refers to Cross Linked ETFE Polymer (Tefzel) which provides increases abrasion resistance over Tefzel insulation. Dual wall construction is commonly used in aircraft. ETFE is described as a "modified radiation cross-linked polymer".

Alternative to MIL-W-22759/44 "Spec 55" Primary Wire

A less expensive and more commonly available wiring is the single wall Tin Plated (TC) Copper strand wiring MIL-W-22759/16. It could be argued that silver has a better conductivity and higher temperature rating than tin plating...but both offer increased protection against corrosion over bare copper wires.

The main benefit of Spec 55, MIL-W-22759/44, over the alternative MIL-W-22759/16 is that it is "tougher" i.e. it has better abrasion properties due to its irradiated jacket. This is less of a concern if the harness is sheathed in DR-25 heat shrink, which is a common motorsports practice. In short it is an acceptable alternative to the more expensive "Spec 55" wire.

In 20 AWG it weighs 5.18 lbs/1000 feet as opposed to Spec 55 20 AWG which weighs 4.3 lbs/1000 feet. It is also larger in diameter in 20 AWG .060" versus .050" for the Spec 55 wire.

Better plating and tougher wire versus cost savings for the /16 alternative.

Note: Tefzel is Ethylene-Tetrafluoroethylene (ETFE)

Twisted Pairs

Crankshaft sensors, camshaft sensors, RS 232 and other communications should use twisted pair wiring. This is available pre-twisted or you can twist it yourself. 20 or 22 AWG is typical for twisted pair sensor and communications.

Twisting the wires reduces magnetically induced interference. Forcing the wires together reduces the loop area and therefore the induced voltage. Since the currents are flowing in minimum loop areas, magnetic field generation is reduced. Good idea to avoid signal problems due to noisy ignitions, coils etc.

Connectors

Deutsch Autosport: Specifically designed for motorsport. Lightweight. Expensive. Requires Mil-Spec crimping and stripping tools.

Deutsch DTM Series : Sealed thermoplastic connectors designed for harsh environments like engine compartments. Reasonably priced. Available from many sources, they offer watertight silicone seals that also act as a strain relief. Available in 2, 3, 4, 6, 8 and 12 pin contacts with size 20 contacts for AWG 16 to 24 gage wire. Either solid pins and sockets or crimped pins and sockets can be used. Solid pins are crimped and are easiest to work with. In no case should the pins and sockets be soldered.

Pictured above are 2, 3,and 4 pin DTM connectors with the optional shrink boot adaptor.

All of the pins and sockets are made from 98% pure copper and then plated. Standard plating is Nickel. For critical circuits, pins and sockets are plated with Nickel and then Gold. For lighting, power and control circuits choose Nickel. For critical and very low voltage and amperage circuits such as oxygen sensors that operate at 0-1 volt or 0-5V (wideband) and for data transmission circuits that operate at 5 volts, choose Gold.

Note: rear silicone seal will seal on smooth insulation from .053" to .120" O.D. Of importance is the fact they are rated at 100 cycles of engagement and disengagement. These are your affordable step below the very expensive Deutsch Autosport line.

Sureseal: Interesting rubber push to connect seals. Like any specific connector they require specific tooling. These connectors are rated at 50 cycles of engagement and disengagement.

Wire Stripping...Thermal

Thermal wire strippers do not nick or cut or scrape the wiring. There are several manufacturers like Teledyne and Hakko. The Teledyne Strippal® Plus pictured to the left above is a self-contained hand-held stripper that either comes with a fixed or variable temperature control. The insulation melts and is stripped cleanly and quickly, readying the wire for crimping or soldering. To the right is the Hakko FT-801 thermal wire stripper.

Wire Stripping...Mechanical

It's best to use a high grade mechanical stripper and not cheap autoparts store ones. On the higher end of the scale the Ergo Elite, pictured on the left, is an excellent wire stripper. The Ideal 45-177 Stripper, on the right, is also an excellent choice.

Crimping Tools

Daniels crimping tools are the defacto standard for motorsports connector pins. We also use specialized tools to crimp Weatherpack connectors and Deutsch connectors.

This is a selection of the crimping tools that we use to make our motorcycle harnesses. Daniels, Delphi, AMP, and Deutsch crimpers.

DR-25 Heat Shrink and Molded Parts

You cover the mil-spec wire with DR-25 heat shrink and transitions are joined with Raychem or Hellerman molded parts, To seal the ends of the transitions or boots there are two options: Use adhesive lined boots (expensive) or use syringe-applied Resintech RT125 black epoxy on the connector or the DR-25 wire cover. The shrink ratio is 2-1 or, in some versions 5-1. This environmentally seals the wires and connectors and provides a protective layer against abrasion.

To choose a size of DR-25 for your harness sections choose the largest size that will shrink firmly to your wiring cross-section diameter. In other words if your wiring bundle is 3/8" in diameter you don't use 3/8" DR-25 as it has a shrink ratio of 2:1 (.375 start to .1875 final). The above dimensions are for several diameters of 20 gauge Spec55 wires, .058" in diameter.

An alternative to DR-25 is Raceline 150 from Whitmor Wirenetics. Basically the same specifications you just don't get "DR-25" printed in yellow. We all know how important labels are these days.

A second source for a less expensive alternative to Raychem DR-25 is Deray V25 from DSG-Canusa.which also has the same 2:1 shrink ratio as Raychem DR-25.

Concentric Twist Layers

The stiffness of the harness will depend largely on how the underlying wires are arranged. The correct method is concentric twisting where successive layers are twisted in opposite directions...One wire surrounded by six wires, with each successive layer adding six additional wires i.e. 1-6-12-18. The twisting of the wires gives the harness additional flexibility and reduces strain on the wires. The above table provides some insight into the methodology.

Wire to Wire Splices

Wire to wire spilces an be accomplished with Tyco Raychem D-406, or Sumitube W79 adhesive lined shrink tube. Do not solder the wires together. Proper crimping is the preferred method. Alternatively, unshielded butt connectors can be used and sealed with adhesive-lined heat shrink. Often wires will branch i.e. 1-2, 1-3 etc. and splices are necessary.

Raychem part # D-406-0001, Red in color, marked "Duraseal 18-22" is the one we use for our "Spec 55" wiring.

Tying or Lacing Wire Harnesses

Mil-T-43435B Lacing Cord: Braided nylon lacing cord meeting specification MIL-T43435B, Type 1, Size 3, Finish B. A micro-crystalline wax with melting point above 55/ C ° 130° F and nonflaking characteristics it is compounded to develop excellent knot retention, yet not giving a waxy feel to the user. Used to tie wiring bundles together. Less bulky than plastic tie wraps which can actually cut into wires and, when cut, leave a sharp edge that can cut your hands.

Continuous loops should tied in the above manner with continual lock stitches. Normally you just put a wrap and a square knot every 6-12".

Wire Spoon

After you've laced your wire harness together with neat little square knots, how do you insert extra wires? The answer is a wire spoon for SteinAir. Note that all the wires are white which is a normal practice in many applications. Spec 55 wire is normally available in 10 colors which makes keeping track of things much easier. Without laser-marking of each wire it can be a real chore to track down issues when all the wires are white.

For your information a typical late model Harley-Davidson Touring bike uses about 77 different wire colors (color and stripes) in its wiring harness.

Portable Thermal Printers

You can, however, label each wire with 1/8" 3:1 heat shrink labels near the terminations to keep track of things and use one color mil-spec wire. Low end heat shrink printers can be purchased way under $100.00 or you can spend many thousands of dollars on commercial units.

BEE3 unit from K-SUN pictured above is about as cheap as it gets. It prints on 1/8" (single MIL-SPEC wire) and  3/16" wire shrink tubing however. It also prints labels in widths of 1/4", 3/8", 1/2" and 3/4" widths. Use either KYNAR or Tyco Raychem RT-375 clear 2:1 heat shrink over your printed labels.

The Kroy 5100 will print wire shrink tubing up to 1/2" I.D. and flat labels up to 1" in width. These are in the range of $395.00 retail.

Wideband Sensor Wiring

The Bosch LSU-4.2 (left) or the NTK (right) wideband sensors are typically married with six position Deutsch DTM connectors. In that they are five wire sensors the sixth poisition uses a seal plug. Wiring colors for the different sensors is as follows:

Bosch LSU-4.2 Typical DTM positions: DTM Terminal 1, Red Wire, WB_Pump; DTM Terminal 2, Black Wire, WB_Cell; DTM Terminal 3, Yellow Wire, WB_Com; DTM Terminal 4, White wire, WB_Htr-; DTM Terminal 5, Gray wire, WB Htr+; DTM Terminal 6, seal plug.

NTK L1H1 Wire Colors: Yellow Wire: 12V; Blue: Heater Wire; Black: Signal Ground; Grey: Nernst Cell Voltage; White: Ion Pump Current.

NTK L2H2 Wire Colors: Yellow Wire: 12V; Blue: Heater Wire; Black: Signal Ground; Grey: Nernst Cell Voltage; White: Ion Pump Current.

Automotive 30A Relays

We use Hella or Bosch 30 Amp relays in our wiring harnesses. This is a pictorial reference as to how they work.

Corrosion Protection

At the Bonneville Salt Flats the salt air and salt eats everything. Internal cavities in relays turn into green gardens. Starter relays and switches die sooner or later. Cadmium plated hardware corrodes quickly. Battery terminals and any metal exposed that isn't stainless or chrome plated begins its ugly descent to mother earth from whence it came.  Boeshield T-9 is the best thing we've found to protect metal surfaces. WD-40 seems to disappear after a time. This stuff stays.

Literature

Motorsport Wire

Raychem Spec 55 Wire (XLTFE Polymer) The standard for high end motorsports wiring.

Mil-STD-861 Color Codes For Mil-Spec Wiring. 100 possible combinations. 10 colors are normally available.

Wire Covering

DR-25 Heat Shrink Used to cover ETFE wires in wiring harnesses. Has a 2-1 shrink ratio. Single Wall. Motorsports std.

DSG-Canusa Deray V25 a less expensive alternative to DR-25

Raychem RT-375 Clear heat shrink tubing. Use to cover your yellow/black wire heat shrink labels.

Kynar Clear Heat Shrink Tubing to cover wire and cable heat shrink labels.

Tyco_RBK_Dual Wall Adhesive heat shrink. Used to seal wire transitions and connectors. Less flexible than ATUM. Strain relief.

Raychem SCL Heat Shrink Used to seal shapes like switches and relays in lieu of specific "boot". Adhesive lined. 2.5:1 shrink ratio.

Tyco ATUM_semi-flexible Adhesive-lined heat shrink. Sealing Boots and transitions and shapes. 4-1 shrink ratio available. Here a three wire Cherry Hall Sensor has 1/4" DR-25, Resintech RT125 epoxy sealing the DR-25 ends, and 16mm ATUM semi-flexible adhesive shrunk to the assembly.

DSG-Canusa CDR Adhesive lined shrink tube. 4:1 shrink ratio. Semi-rigid. More rigid than Tyco ATUM. Splice covering.

DSG-Canusa CPA Adhesive lined shrink tube. 3:1 shrink ratio. Connector sealing.

Molded Parts

Raychem Molded Parts Heat Shrinkable, adhesive-lined, for wiring harness transitions and connectors.

Hellermann-Tyton Molded Shapes, Heat shrinkable up to 5-1 ratio shapes for transition and connector sealing.

Resintech RT125 Wiring Harness Epoxy.

Wire Stripping

Tyco Wire Stripping Guide

Teledyne Stripall Thermal Stripper

Ideal Wire Processing (Stripper) Catalog

Circuit Breakers