Legacy Harnesses

Kustom Truck Parts' Legacy Harnesses provide a proven, cost-effective solution for mechanical-to-electronic engine conversions in heavy-duty trucks. Designed specifically for upgrading older mechanical engines (like Cummins Big Cam/Small Cam, Caterpillar B/C models, or Detroit 6V71/8V71) to modern electronic ones, these complete harness kits bridge the engine-to-cab interface without replacing your entire wiring system.

Unlike chassis-specific NAMUX harnesses, Legacy solutions are generic and versatile—fitting virtually any make or model (Peterbilt, Kenworth, Freightliner, Western Star, International, Volvo, etc.) with a mechanical engine. Each kit includes: Engine-to-Cab Harness (ECM to firewall): Routes power, data, and sensor signals from the new electronic engine into the cab. Dash-Side Add-In Harness: Overlays onto your existing gauge/switch wiring, adding essential electronic feeds for features like cruise control, Jake brakes, fan override, and AC high-pressure monitoring—without unnecessary rewiring.

These harnesses pair seamlessly with our Switch/Sensor/Label Kits (for check engine/stop engine lamps, cruise, engine brake switches, fan override, and various sensors) and Electronic Throttle Pedal kits (with pre-installed TPS and extension harness for precise throttle response) for a complete electronic interface package.

Legacy Harnesses deliver reliable, OEM-style connectivity, modern diagnostics, improved fuel efficiency, and enhanced performance—making electronic upgrades straightforward and affordable. Ideal for fleets, mechanics, and owner-operators seeking a complete cab-interfacing solution. Explore our Legacy Harnesses collection for the exact match to your Cummins, Caterpillar, or Detroit electronic engine project.