Project Lexus SC300 Road Racer: Part 8 - Planning for Performance

by Erik Jacobs


So far in the epic rewiring saga of Project SC300 we’ve managed to write thousands and thousands of words, and we don’t even have any wires pulled or harnesses assembled. It just goes to show how much work and planning goes into doing wiring right. While there is still a lot of fabrication to be done and little odds and ends to take care of, it’s time to talk about planning a wiring job. Get your reading glasses ready- this article is going to get wordy.

We didn’t just start randomly cutting panels and laying wire, figuring it out as we went along. In Part 4 we decided on a number of electronic components. Throughout the last few segments we have mentioned wires and currents and different considerations for circuits, but how did we get there? Well, it all starts with your plan.


Here’s our friend the Racepak Smartwire.

The Smartwire will be distributing power to almost all of our major systems. There are a few circuits that we did not remove from the existing Haltech plug-and-play harness. However, the Smartwire is generally the heart of our wiring system. Well, maybe it's the lungs. We already said the XS Power battery is the heart. Okay well, it's a really mission critical system.

We chose this system because it offers a good number of inputs and outputs, has prewired switch options, and has an attractive cost. But how did we decide what to do with all of those inputs and outputs? It all started with a wishlist.


Here’s Ed Senf again. The quick recap on him: decades of experience planning, designing and installing motorsport electronics systems, tuning and calibration, championships in World Challenge, Rolex/Tudor/Continental, and all that. He knows a thing or two when it comes to wiring.

Ed and I have had a lot of conversations about what is going into Project SC300, and something he always says comes to mind, "the journey is not always about the destination."

My wishlist was a little silly. I wanted a race car that could be street legal and “all weather”. That meant:

  • It needed fully functional lights: both high- and low beams, brake and tail lights, reverse lamps, blinkers and hazards.
  • It needed a horn- what race car doesn’t?
  • It needed to retain the factory powered in/out up/down steering column.
  • It needed both a speedometer and a tachometer- the car actually didn’t have either of those working previously.
  • It needed functional wipers, but we settled on one speed (high).
  • It needed a "cat" to pass emissions so that it could be registered for the street in Georgia.

Do I expect to drive a caged race car on the street often? No. But then again, the alignment shop is not far from my house and it sure is easier to drive there than to go through the rigamarole of loading it on the trailer!

Do I expect to be doing any racing or driving at night that would require lights? No, not any time soon. But why shouldn’t the headlights and blinkers work? Many racing organizations and track day groups require functional tail lamps and a couple of extra things that couldn’t hurt.

Won’t I be the primary driver? Yes. But it’s nice to be able to retain the factory adjustment to be able to accommodate multiple drivers, so the power steering column remains.

Every vehicle needs Hella Supertones. Period.

Racing doesn’t stop because of a little rain, so wipers were a must regardless of whether or not the car was streetable.

Of course the engine running gear needed to be powered. That’s a given.


This wishlist provided for a good baseline for the plan.

Since I’m a bit of a computer nerd, and wanted to keep track of things and make everything easy, I went ahead and made a spreadsheet using Google Docs. This let me share with Ed and others that needed to provide input or insight.

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Dan DeRosia
Dan DeRosialink
Wednesday, January 25, 2017 4:47 AM
Really enjoying this stuff - been looking into doing a professional grade harness for a race project of my own, and after seeing all the professionals make things look easy, it's good to see ... someone closer to my own skill level, if you get my drift.
Wednesday, January 25, 2017 6:06 AM
@Dan - thanks for the feedback! We are definitely trying to make the daunting seem possible with this project. In the next few segments as we assemble each sub-harness we'll also be going into more detail on why we made the choices we made for that particular bit.

I've been contemplating some kind of "universal" harness constructed like this, but haven't really figured out how to make it make sense. Basically you would just add your own connectors on each end.
Dan DeRosia
Dan DeRosialink
Wednesday, January 25, 2017 10:15 AM
I find that I kind of waver between "holy cow is that complicated" and "... wait a sec, if I break down the steps it's not that bad" for all sorts of things like this. After having a car I prepped (for my dad; I'm not a professional) have a minor electrical fire one race, I've been on the lookout for ways to improve, you know?
Wednesday, January 25, 2017 11:37 AM
wowzers! The amount of time it takes to undertake a project like this is crazy. And then you took the time to write out every little detail. Thank you for this! Articles like this are the reason I check MotoIQ every morning. Keep up the good work, I can't wait to see the next post.
Dang Le
Dang Lelink
Wednesday, January 25, 2017 2:19 PM
Big fan of wiring harness builds. The tools alone for building them can get pretty expensive, and put some people off. Thanks for posting updates to Project SC300, and for the details of what goes into building a proper car.
Thursday, January 26, 2017 8:46 AM
I can't see any of the pics from the computer, but a brief google search really makes this sound like kapton wiring is not without its flaws.


The KC-135 uses teflon insulated wiring and while a little thicker than the F15's kapton wiring, doesn't light up like the 4th of July as it ages. The outer colored layer of insulation eventually starts to flake off and you're left with the inner copper colored layer.
Thursday, January 26, 2017 4:20 PM

I can't speak to Kapton, but rather only ETFE, which is what Spec55 is coated in (Tefzel). Here's more chemical information on ETFE/Tefzel:


From the same site, different page:


"Tefzel™ is a modified ETFE (ethylene-tetrafluoroethylene) fluoroplastic available as pellets or as powder for rotational molding. Tefzel™ ETFE resin combines superior mechanical toughness with an outstanding chemical inertness that approaches that of Teflon™ fluoroplastic resins. Tefzel™ features easy processibility, a specific gravity of 1.7, and high-energy radiation resistance. Most grades are rated for continuous exposure at 150°C (302°F), based on the 20,000-hr criterion."

Chemours says that ETFE is rated "V0" on the UL94 test. According to the following:


UL94 V0 is "self extinguishing (best)". More specifically V0 means:

"Burning stops within 10 seconds after two applications of ten seconds each of a flame to a test bar. NO flaming drips are allowed."

Do you have any further information to back your claim, or a reasoning for using wire constructed to a different specification? MIL-W-22759 and specifically Raychem Spec55 is used on pretty much every professional race car you have seen driving on a track in North America, and in upper levels of motorsport worldwide.

Wikipedia says the following about the F-15 (https://en.wikipedia.org/wiki/McDonnell_Douglas_F-15_Eagle):

First flight 27 July 1972
Introduction 9 January 1976

And, regarding Kapton (https://en.wikipedia.org/wiki/Kapton) -- it was designed in the '60s.

Given that Spec55 is not Kapton, I am not particularly concerned with Kapton's shortcomings.

Here's the Wikipedia page for Tefzel/ETFE, if you're interested:


@everyone else -- Thanks so much! This has been a really, really hard project and I am really looking forward to finishing documenting it for all of you, and to finishing it!
Friday, January 27, 2017 9:58 AM
I only speak from experience with kapton. I realize technology moves on, I was only trying to warn you of the potential here. A race car sees a lot of heat and vibration like a fighter jet. Kapton is still used today, perhaps it was only the older stuff that liked to light itself on fire. It still would make me hesitant to use a coated wire. What's the life expectancy of wiring like this in a race car?
Dusty Duster
Dusty Dusterlink
Friday, January 27, 2017 11:03 AM
Cool to see we have another EE contributor!
Friday, January 27, 2017 11:10 AM
@Supercharged111 I can't say, and I was not trying to go on the offensive. As far as lifespan goes, I don't think there is a defined service life. If I remember correctly, Porsche uses this type of wire when they build their GT race cars at the factory. I will double check on that for you.

A race car in certain areas may see a lot of heat and vibration, but a fighter jet is on another playing field all together when it comes to those two things.

I would think that on a club level race car, even an endurance car, that sees 6-10 weekends of use, you would get many, many, many years before a harness failure would occur due to wiring problems specifically related to ETFE. Given that this is the military's current specification for aerospace wire and given the expected service life for most military vehicles, I would think that on an occasional use race car you are more than covered.

The other thing is that most race cars don't have a very long service life. Upper-level teams are building new cars and doing net-new wiring every year, and many of those "former" cars go on to live long lives as club level race cars without ever being touched again.
Tuesday, February 07, 2017 7:03 AM
Kapton insulated wire isn't widely used in automotive applications (none that I'm even aware of), and it is hardly used in commercial aircraft anymore. It was banned for use by the U.S Navy in 1987, and Boeing stopped using it in 1992 (they are responsible for more than 90% of the worlds commercial aircraft). There is a newer variant of insulation called TKT that is a Teflon wrapped Kapton variant, but again, not used in automotive applications. Tefzel is the industry standard in motorsport at all levels, period. As Erik mentioned, it will actually extinguish itself if it is exposed to direct flame, hence why it is so popular in motorsport, defense and aerospace industries. In fact, M22759/32 wire is used in over 95% of all the defense projects we build harnesses for and 99% of the motorsport harnesses we build.

Regarding the life span of a harness in a race car, one thing that we do is Cirris HiPot test harnesses for customers at random intervals. Some teams will mileage out a harness to get tested, and some will just have it tested once a year during the off season. Even without that type of testing, a properly built harness should last many years in even the harshest environments. We regularly see race cars that have harnesses we built well over a decade ago still working as well as they were when they were put into service.

It is a wise investment to do your vehicle wiring the right way the first time. If you have ever had an electrical problem at the race track, you already know what I mean. If you haven't had an electrical issue at the track, consider yourself lucky and take the proper steps to continue that tradition!

Great article and good discussion everyone! Always great to chat about mil-spec stuff :)

Monday, June 05, 2017 9:03 AM
Any way you could share your planning document? I'm trying to layout a new harness for my SC400 race car, and I'd love to have some more excel pages to reference for laying out the circuits. This whole series has been awesome.
Tuesday, July 04, 2017 7:05 AM
Greg - I didn't forget about you.

Please find me on Facebook and send me a message. I'll be happy to make a copy of the sheet and send it to you. There's some "private" info in it right now but that'll be easy to clean up.
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