Getting Ready to Trim Down the Wiring Harness | Project LS-Powered 350Z

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Update by Tom Suddard to the Nissan 350Z project car
Jan 18, 2021

Controls in place, we could at least push our LS-powered 2003 Nissan 350Z around the garage. But driving was the goal, so we needed to work on reinstalling the wiring next. The car’s body wiring harness, all 13.4 pounds of it, was still bundled up in a plastic bin in the corner of the garage, and the car wouldn’t run without it.

Here we faced a dilemma: Under the hood we had a plug-and-play engine-swap harness from LOJ Conversions, but it relied on its connection to 350Z’s body harness to run. In theory, we could cut away 90% of the wires (and weight) from the OEM body harness, leaving only what was necessary to run the LOJ harness connected to the engine, along with the ABS and lights. Why cut out so many wires? It saves weight, space and complexity, and means searching through 10 wires instead of 100 when we have a problem at the track.

One problem: Cutting down a harness is not a quick and easy process, and once you remove a few dozen wires it’s tough to go back. We’ve actually been down the “thin out a factory harness until you’re left with a race car harness” path before, and it’s easy to get ahead of yourself and make mistakes if you’re not careful.

How can you be careful? There are two methods, and the first is gaining a complete understanding of every single circuit in the harness and near-memorization of the factory wiring diagrams. The second method (and the one we’d be using) is to get the car running and driving on the full harness, then slowly unplug and cut things until you screw up while using the factory diagram as a guide. That’s how we found ourselves stuffing the entire body harness into the passenger footwell, trying our best to contain its extra bits and pieces with a billion zip ties. We left 75% of the connectors unplugged, and assuming our first test day goes well, we’ll label everything we are and aren’t using, lay the harness on the bench, and trim it down to the bare necessities. Try not to judge us while we finish the rest of the interior around this rat’s nest, okay?

Harness sufficiently wadded into place, we flipped the switch and pressed start, and the 350Z fired up. The track seemed to be getting closer by the minute.

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350z247 New Reader
1/22/21 8:00 a.m.

If it makes you feel any better, I still haven't gotten around to thinning most of my factory harness on my 350Z track car. There is a similar rats nest stuffed under my chloroplast dash waiting for me to have some free time.

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