Wire Harness Design and Manufacturing

[dvl]

I recently completed building a new wire harness for my Seven, using manufacturing methods from the aerospace, motorsports, and modern road car industries. I’ve spent the majority of my career in the space engineering domain, so the harness is based on my experiences, learning, and observation of similar work over the past 25 years.  This thread is being started to share my work and collaborate with others doing similar work.  
The design and construction philosophy was to build a highly reliable harness.  From an architecture perspective, all high current functions are relayed (both solid state and traditional), ground side switching is used where pertinent, and the dashboard and chassis harnesses are separate subassemblies to aid in assembly, test, and future repair.  This drove the use of ETFE insulated silver plated copper wire, aircraft type environmental splices, solder where necessary, high quality connectors with crimped pins, fire retardant shrink sleeve tubing, and lacing cord to secure the harness (as opposed to cable ties).

 

I will add more detail, but for now please see the following pictures.  The first image is of the complete dash harness. The subsequent image are some of the main harness fabrication.

 

Thanks,

Dave 

[Vovchandr]

Can you give details on what engine and ECU you're wiring?

Can you give estimates on how long does it take at quickest vs your detailed work?

Any advantages to having a military style quick disconnect that was popular a long while ago in the wire tucking community?

Is re-pinning an option for most people. 

 

I have considered either going to a different ECU or even an an engine swap but the daunting task of rewiring is a big barrier even though I have a harness for the new ECU (already own an Omex but not married to it). 

[JohnCh]

@dvl thanks for starting this thread. It's great timing as I'm just in the beginning stages of rewiring my Elan. Although I'm using the Elan loom from Advance Auto Wire as my starting point (modern GXL wire in traditional British colors, twelve fuses, not two, all relays and fuses in one location, detailed color-coded schematic, etc), the routing and termination methods are on me, and not all are decided yet.  I do plan to use Deutsch Connectors as shown in your photos but hadn't considered lacing cord rather than zip ties.  Am I correct the benefit to that approach is no sharp edges, and no danger of heat and time embrittling the plastic?  

 

Thanks,

John

[dvl]

1 hour ago, JohnCh said:

@dvl thanks for starting this thread. It's great timing as I'm just in the beginning stages of rewiring my Elan. Although I'm using the Elan loom from Advance Auto Wire as my starting point (modern GXL wire in traditional British colors, twelve fuses, not two, all relays and fuses in one location, detailed color-coded schematic, etc), the routing and termination methods are on me, and not all are decided yet.  I do plan to use Deutsch Connectors as shown in your photos but hadn't considered lacing cord rather than zip ties.  Am I correct the benefit to that approach is no sharp edges, and no danger of heat and time embrittling the plastic?  

 

Thanks,

John

Hi John,

You are correct about the benefits of using lacing cord over cable ties. I use cable ties sometimes in harnesses, but generally only those made from ETFE or PEEK, just like in the aerospace industry. The ETFE or PEEK cable ties are also considerably more expensive than lacing cord. 
The Advanced Auto Wire harness sounds like a great option.

Thanks,

Dave

[MV8]

I still have a few types of lacing cord on spools from when I did this type of work. Easy to find the general stuff if you look for wax twine or similar naming. There is no issue with quality zip ties becoming brittle unless they are close to the exhaust but they all should be (carbon) black to resist UV. Mcmaster has a nice variety of wiring accessories and no junk. Waytek Wire is another online source but you must register as a company to buy. Also Aircraft Spruce.

 

If anyone is interested in learning the methods to tie using lacing cord, see FAA AC43.13-1B. Free online pdf so no need to buy the book. Lots of good information in that. 

[dvl]

5 hours ago, Vovchandr said:

Can you give details on what engine and ECU you're wiring?

Can you give estimates on how long does it take at quickest vs your detailed work?

Any advantages to having a military style quick disconnect that was popular a long while ago in the wire tucking community?

Is re-pinning an option for most people. 

 

I have considered either going to a different ECU or even an an engine swap but the daunting task of rewiring is a big barrier even though I have a harness for the new ECU (already own an Omex but not married to it). 

Hi,

This car is powered by a Ford Crossflow engine and doesn’t run a dedicated ECU. It does use modern, but vintage appearing, Spa Design Classic gauges (stepper motor drive and 3-wire sensors), two 4-circuit solid state relay banks by Cartek (UK-based race electrics manufacturer), a hazard flashing circuit, high beam indicator, etc, so there is a considerable amount of wiring in the car.

From an engine and car sensor and warning or gauge perspective, the car has feeds for an oil pressure gauge, oil pressure warning lamp, 4 psi oil pressure switch on the fuel pump circuit, water temp, oil temp, ignition, tach, speedo (GPS pulse to reduce complexity compared to a wheel speed sensor), gauge peak recall selection switch and button, separate indicator and hazard warning lamps, high beam indicator lamp, and a fuel pump oil pressure switch override (prime) lamp.

 

The minimum time to build a harness is about 20 hours of work (long weekend project), as compared to 200+ hours for this configuration.  This harness has 200+ hours of work in it, from sketching out the diagrams (need to remake in Visio), thru routing each wire using the car as a form board, labeling, crimping pins, testing all circuits, removing the harness for lacing, shrink sleeve, and wrapping, etc.  

The first harness I built for the car took about a weekend of work, but only contained enough to run and have functioning gauges and brake lamps. It’s roughly what I would build a vintage race car. 
 

If one can justify the cost, quick discount, MIL-DTL-38999 type connectors are the best option.  They are designed for 1000’s of mate/demates, are lightweight, environmentally sealed, mass produced, and available in countless configurations.  This harness was build to a high end level of quality, but even then I couldn’t justify the cost of new 38999-type connectors. Deutsch DT and DTM connectors are OEM automotive grade, use pins similar to 38999 connectors, are environmentally sealed, and are a good balance of quality and price.

 

Repinning is an option, but requires the right tools. Good quality crimp tools are expensive (approx. $300 each) although lower quality knock-off tools can be found for a lot less on Amazon.   I can always justify the purchase of good quality tools, but between correct wire stripping and crimping tools, the expense adds up quickly.

Building a full harness is a somewhat daunting and time consuming task, but is relatively simple if you do it one wire at a time and have the right tools. 
 

I hope this helps,

Dave

[CBuff]

I ordered some mil spec wiring from motecs subdivision 

 

https://www.milspecwiring.com

 

it’s pricey but seems indestructible. Should my car burn to the ground I have visions of the wiring being intact in the charred remains. 
 

The sheathing does take some sharp strippers and you have to err on the smaller size for shrink connectors so you get a good seal on the smaller sheathing.  

[Marek]

Thanks, Dave, for starting this thread.  I am just now sourcing materials for a similar project.  Could you share sources?  My own experience was a 6 year career detour into professional sportscar racing.  I started in data engineering and driver coaching and it later evolved into all manner of car electronics and harnessing.  I still have my Daniels crimpers and other tools, but have found my parts sources are out of date.  Recently, I've been using prowireusa.com as well as milspecwiring.com.

 

I see you chose CarTek PDMs - I am curious why they were your preference.  I don't see a fuse or breaker box in your pictures.  What route did you choose for circuit protection?

 

For anyone looking for a good background read, I recommend https://www.rbracing-rsr.com/wiring_ecu.html.

[Joe Petty]

My S2 7 was raced and most of the wiring was ripped out and since it was completely apart I figured it was best and easiest to rewire the whole thing.

I wanted to stay pretty much original (Positive ground, Generator, Points/Condenser...) but avoid what I felt were some of the common problems.

There are several wiring diagrams available, so I looked for the one that seemed to fit my car: no heater, cooling fan switch, mechanical fuel pump...

 

A used MGB wiring harness from eBay cleaned up nicely and provided all the correct colored wire I wanted in adequate length and sizes.

No burned or brown spots were found, and cutting off a few inches usually got to nice clean copper.

 

All connectors (bullet and slide on) were replaced and soldered.  I don't trust that cut, strip and crimp tool that comes in the box of crimp connectors!

I grew up in the Keys and dealt with a lot of corrosion/connection problems, even soldered wires to bulbs a few times!

 

I have never liked the way Lotus ran the headlight power through multiple switches.  I planned to use upgraded headlights, so the headlight power was used to control fused relays situated close to the battery and saved adding an additional fuse block.

 

Wiring a 7 is surprisingly simple once you set your mind to it.  Particularly the early ones where most of the gauges are mechanical and there are few "accessories".

 

Good Luck - Joe

 

[dvl]

10 hours ago, Marek said:

Thanks, Dave, for starting this thread.  I am just now sourcing materials for a similar project.  Could you share sources?  My own experience was a 6 year career detour into professional sportscar racing.  I started in data engineering and driver coaching and it later evolved into all manner of car electronics and harnessing.  I still have my Daniels crimpers and other tools, but have found my parts sources are out of date.  Recently, I've been using prowireusa.com as well as milspecwiring.com.

 

I see you chose CarTek PDMs - I am curious why they were your preference.  I don't see a fuse or breaker box in your pictures.  What route did you choose for circuit protection?

 

For anyone looking for a good background read, I recommend https://www.rbracing-rsr.com/wiring_ecu.html.

Hi,

For material sources, I use the following. Most of my wire, flame retardant shrink sleeve, and environmental splices (expensive butt connectors that require a dedicated tool from Daniel’s), boots, lacing cord, etc comes from Aircraft Spruce.  Race Spec has a great cross section of wire, connectors, fuse boxes, tools, etc in stock. Pro Wire USA has been my primary source for Deutsch connectors.  Pegasus is a great general source for wire, PDM’s, and other supplies.  McMaster-Carr takes a lot of my money too.  Bel-Metric is my source for double crimp OEM-type double crimp spade connectors.

https://www.aircraftspruce.com

https://racespeconline.com

https://www.prowireusa.com

https://www.milspecwiring.com

https://www.mcmaster.com

https://belmetric.com/electrical/double-crimp-spade/

 

I chose to use two Cartek 4-circuit PDM’s for simplicity, sparing, and experience purposes.  There’s a spare Cartek unit in my toolbox, if ever needed.  I seriously considered using a Motec PDM15 or PDM30, but felt that it was overly complex for such a basic car. In retrospect, a programmable PDM would have simplified some of the more complex hard-wired circuits in the car, such as the interaction and isolation of the flasher and hazard circuits or the fuel pump power circuit that turns on with the ignition, but shuts off if oil pressure is below 4 psi (but can be bypassed for starting and includes a bypass warning lamp).  I designed and built the harness as two subassemblies; (1) power distribution and dashboard and (2) chassis harness. With that architecture, it gives me the option to change to a completely different PDM system, by rebuilding the power distribution and dash harness.  
 

I first started using the Cartek units, years back, to build a simple power distribution circuit for a vintage race car (ignition, starter solenoid, fuel pump, and electric fan).  All of that being said, I should buy a Motec or equivalent unit to play with.

One benefit of the 4-circuit Cartek PDM is that they are the same footprint and bolt pattern as a Lucas 7FJ 4-circuit fuse box. Cartek doesn’t mention it in their instruction booklet, but I assume it was originally designed to replace the Lucas 7FJ unit. For fusing and power distribution of circuits in my car, there is a Lucas 7FJ mounted on the opposite side of each Cartek unit (if one looks under the dash, they see two classic style Lucas fuse boxes).  As a functional example, one circuit on a Cartek PDM is for ignition and is ground side switch enabled by a dash mounted ignition switch. The Cartek unit acts as an ignition relay and 10A breaker for the circuit. The ignition output from the Cartek unit feeds into a Lucas 7FJ.  I have 4 fused ignition circuits that feed from the 7FJ.

I hope this helps,

Dave
 

[Marek]

The sources are much appreciated.  I especially like your modular design.  I am hesitant to over engineer the electrics in my car and going modular would be a good way to modernize yet keep maintenance within reach of a future owner.

 

The Cartek is very simple, highly reliable, and very affordable.  I understand the attraction.  I've looked at the AiM, Motec, Blink Marine, and MicroPDM PDMs as well.  Motec is always a great choice.  But with a MicroPDM I could easily afford to carry a spare.  Tough choices.  The integrated logging of the AiM boxes is interesting as I would like to look at improving the engine and charge cooling in this car and logging would be a big help.