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Building an Engine Wiring Harness - Rip It, Strip It, Lay It, and Wrap It

Scott Tsuneishi
Jun 14, 2013

Whether you need to customize your engine wiring harness or just want to improve its appearance, we offer an alternative to purchasing expensive aftermarket harnesses. Keep in mind that this is not a definitive guide on building wiring harnesses; rather, we show you some basic steps on how to properly restore/clean up your engine wire harness using a number of DEI products.

01 building engine wiring harness Photo 2/24   |   Building an Engine Wiring Harness - Rip It, Strip It, Lay It, and Wrap It

If you've noticed by now, the OE harness has been sheathed using electrical tape and plastic loom. Yes, it's cost effective on their part, but in all honesty, it doesn't look good. The factory-style split loom is an eye sore with its bulky appearance while electrical tape over time will "weep" adhesive and peel off, leaving a sticky residue that's a nuisance to remove.

The most important thing to consider before tackling this particular DIY project is deciding if this is a full-blown rewire job or a simple clean up. The more time-consuming wiring jobs will take a few days to a week to complete, so if this is your daily driver plan accordingly. Upon spending some time researching different methods of making wiring harnesses more clean and subtle, we decided to loom the harness entirely in heat-shrink tubing (no seams). We began by spending some quality time peeling off about a roll of old, greasy sticky, electrical insulation tape from our Subaru STI engine harness.

Wiring Harness Rebuild

06 building engine wiring harness plug Photo 6/24   |   Building an Engine Wiring Harness - Rip It, Strip It, Lay It, and Wrap It

It's important to use the proper tools: a good set of wire strippers and cutters, a soldering iron, a heat gun, shrink wrap, pick tools, and self-vulcanizing tape. Always keep an OE service manual handy to access the wiring diagrams for your vehicle's exact year and model/sub-model due to wiring differences between models. Repair any frayed wires prior to rewrapping.

05 building engine wiring harness wiring diagram Photo 7/24   |   Building an Engine Wiring Harness - Rip It, Strip It, Lay It, and Wrap It

Document the current wiring/clips and routing with detailed pictures prior to de-pinning the harness. If necessary use masking tape and/or zip tie to separate the wires and label each connection prior to taking photos for future reference to keep track of your progress. Most importantly, don't begin by simply tearing apart your engine harness! Carefully plan your route of attack while sorting through the tangled wires. Properly measure each wire length as well as how they are routed to ensure your finished harness will install properly without any issues.

Heat shrink offers a clean, no seam look, and it will never peel off or break. The DEI heat-shrink tubing is mil-spec grade, withstands up to 275 degrees F of direct heat, and is flame retardant. This meets or exceeds the corrugated looming that you typically see on engine harnesses.

07 building engine wiring harness wiring Photo 8/24   |   Building an Engine Wiring Harness - Rip It, Strip It, Lay It, and Wrap It

DEI Hi-Temp Shrink Tubes

DEI Hi-Temp Shrink Tubes can be used to insulate wires, wire splicing, connections, and terminals and meets the material functional properties of mil-spec DTL-23053/5C. Professional-grade mil-spec flexible polyolefin tubing provides excellent electrical insulation, protection from dirt, dust, solvents, and foreign materials as well as providing strain relief. With a 3:1 shrink ratio and temp resistant from -67 degrees F to 275 degrees F, DEI shrink tubes are an alternative to corrugated plastic, which over time will cause "chaffing" of wires inside the conduit. It is best to have your wires tightly wrapped with heat shrink so they do not rub against each other. A simple trick to speed up the process is to use a wire secured to tape holding the main wires to pull through the heat-shrink tubes.

DEI Fire Tape

Fire Tape is a nonadhesive silicone rubber tape that is self-bonding, self-curing, and forms a permanent watertight barrier that withstands 475 degrees F direct continuous heat. We like the fact that you're not left with a sticky residue when unsheathing the wires. Combined with the DEI Fire Sleeve or hose protective sleeve products is an excellent insulating alternative to vinyl tapes and can be used to wrap wiring harnesses and cover and protect wire splices. Problematic portions of the harness, such as the firewall plugs that are too large to fit heat-shrink sheathing over the wires have the option of being rewrapped in loom/tape or nonadhesive silicone rubber tape as we used in the photo at the left.

14 building engine wiring harness DEI fire tape Photo 15/24   |   Building and engine wiring harness

DEI Fire Sleeve

19 building engine wiring harness DEI fire sleeve Photo 19/24   |   Building an Engine Wiring Harness - Rip It, Strip It, Lay It, and Wrap It

Constructed from a high-temperature-resistant braided glass material, woven into a sleeve and heavily coated with 100 percent iron oxide silicone rubber, Fire Sleeve provides the ultimate in heat insulation and protection from direct heat up to 500 degrees F continuous/2,000 degrees F intermittent heat. The fire sleeve helps to insulate wiring, hoses, oil/brake/transmission lines and can also be used for bundling and protecting hoses, electrical wiring, and more. To dispel heat, we wrapped the ignition coil wires with DEI Fire sleeve, which happens to sit adjacent to the turbo up-pipe.

18 building engine wiring harness DEI fire sleeve Photo 20/24   |   Building and engine wiring harness

Fire Wrap 3000

Constructed from the same material as Fire Sleeve but with the convenience of a hook and loop edge closure design. Simply wrap Fire Wrap 3000 around wires, cables, or hoses without the need of disconnecting. We plan to cover the larger harnesses in the direct path of the turbo and downpipe once our newly rebuilt engine has been installed.

23 building engine wiring harnessfire wrap 3000 Photo 24/24   |   Building an Engine Wiring Harness - Rip It, Strip It, Lay It, and Wrap It

Using a labeler can help identify plugs when installing them on your engine. You can take it one step further and use clear heat shrink to protect the labels.

We think the results are pretty nice and make for a really clean look, but you can be the judge.

Sources

DEI
Avon Lake, OH 44012
440-930-7940
www.DesignEngineering.com
By Scott Tsuneishi
247 Articles

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