Project SC300 Road Racer: Part 12 - Cabin Fever

by Erik Jacobs


The trunk harness was complete. The engine bay harness work and modifications were complete. Now it was time to finally get after the main cabin. And, oh what a project it would be. Let’s take a look at our cabin harness diagram to see everything that we’ve got going on:


The cabin harness is, by far, the most complicated part of the project.

The cabin harness has quite a few circuits, and actually is composed of a big harness and a few sub-harnesses. Starting with the simplest harnesses, we have an ECU bridge harness:


The ECU bridge harness makes it easier to integrate the Haltech Elite 2500 with our new wiring and the existing Haltech plug-and-play harness.

The bridge harness has four functions:

  • It brings any “new” signals and functions out of the Haltech ECU’s connectors to a dedicated DTM for integration with the main cabin harness
  • It allows for any unused signals and functions to go to a “spares” connector in case we want to do interesting things in the future
  • It has a dedicated wheel speed sensor connector to go to the pulsed inputs on the Haltech
  • It has a dedicated CAN connector for integrating with our other devices


Building the bridge involves tearing up some of the plug-and-play harness.

The plug-and-play harness had existing connections for various auxilliary devices and other in-cabin functions that we would not be using as-is. So, we pulled these unused connections out of the harness and main Haltech connectors. Where it was trivial or simple, we clipped or removed harness sections. Otherwise, we clipped them and shrunk them out of the way.


Get your act together and then get in motion.

As always, we pre-cut all of our wires to the right length, get them organized, and then start stripping and crimping. The knock sensor connections should use shielded cabling, so this sits in waiting in the front of the picture.

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Wednesday, January 10, 2018 1:16 AM
stupid question maybe but i have to ask ... why did you wire the can sensors that way ? It is a bus, so you can daisy chain sensors, no need to wire them all in paralel and join it all at the ECU. Or did i miss something ?
Wednesday, January 10, 2018 6:11 AM
So, we don't have any CAN "sensors" on this project, although such things do exist. I think you meant to say "devices" or similar, so I'll go with that.

When you think about a "bus", or parallel wiring, it's basically what we did.

Graphically it looks a little like this:


Sure, the ECU is the *, and we've split off in a few places, and we could have done something like:


Electrically they are equivalent. However, our circumstances made the former "split" style a little more preferable:

* We wanted a sniffing/resistor port near the ECU
* We were using the Haltech CAN hub at least for the WBC1/wideband
* The data logger was "over there", while the ECU and the WBC1 were sitting practically on top of one another.

We could have wired the ECU directly into Haltech's CAN hub, plugged the WBC1 into the CAN hub, and then made a cable to plug our logger into the CAN hub. If we needed a sniffing port, we could have plugged directly into the CAN hub as well.

This is the nice thing about CAN -- because it's a simple two-wire electrical bus, just about anything will work as long as you use quality twisted pair and appropriately handle termination resistance (either with the devices themselves or with actual resistors wired in at the correct location(s)).
Thursday, January 11, 2018 5:41 AM
Thanks for the explanation.
I knew it was equivalent, i was wondering why not use the convenience of daisy chaining the devices instead of wiring them like a hub. It makes sense to wire it as a hub if devices are not near each other :)
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