Holley EFI Gen III HEMI Early Coil Harness

2003–2018 Chrysler 5.7L / 6.1L / 6.4L HEMI Engines

558-310

Overview:

The Holley EFI Gen III HEMI Early Coil Harness is engineered specifically for Chrysler’s 5.7L, 6.1L, and 6.4L HEMI engines produced between 2003 and 2018. Designed to work with the early coil style that requires spark plug wires, this harness enables precise control over fuel and spark timing when paired with Holley EFI systems. Ideal for enthusiasts upgrading their Gen III HEMI engines or performing engine swaps, it provides the foundation for advanced tuning capabilities and enhanced engine management.

This harness is perfect for those seeking to maximize performance with power adders such as nitrous oxide, superchargers, or turbochargers, and it supports alternative fueling methods including methanol and water injection. With Holley EFI’s cutting-edge technology, users gain full command of their engine’s fuel delivery and ignition timing for optimized power and efficiency.

Key Features:

Built to meet the demands of high-performance Gen III HEMI engines, this harness offers reliable connectivity and durability. Key features include:

• Designed specifically for early coil setups on 5.7L, 6.1L, and 6.4L Gen III HEMI engines (2003–2018)
• Enables full control of fuel and spark timing with Holley EFI systems
• Compatible with power adders such as nitrous, superchargers, and turbochargers
• Supports methanol and water injection tuning strategies
• TXL grade copper wiring for minimal weight and high-temperature resistance
• Factory-style terminations ensure secure, reliable connections
• OEM-grade connectors provide precise, positive fitment
• Harness routed through split-loom braid for protection and clean appearance
• Simple identification of coil type via plug wire requirement for easy installation

Construction & Design:

The harness is constructed using premium TXL grade copper wiring, known for its excellent conductivity and lightweight properties. This wiring is encased in a high-temperature sleeve with a small diameter to reduce bulk and improve routing flexibility within the engine bay. The use of factory-style terminations and OEM-grade connectors guarantees a secure, vibration-resistant connection that matches or exceeds factory standards.

Routing through a split-loom braid not only protects the wiring from abrasion and heat but also delivers a professional, clean look that complements the engine bay. Every aspect of the harness is engineered to fit the Gen III HEMI engine platform precisely, ensuring a hassle-free installation and long-lasting performance.

Installation & Fitment:

This harness is designed for direct fitment on Chrysler Gen III HEMI engines equipped with the early coil style, which requires spark plug wires. Identification is straightforward: if your coils require spark plug wires, this is the correct harness. Installation involves connecting the harness to the engine’s coil and ignition system, with no modifications necessary for compatible vehicles. This plug-and-play design simplifies upgrades and engine swaps while maintaining OEM-level reliability.

What's Included:

• Holley EFI Gen III HEMI Early Coil Harness (Part #558-310)
• OEM-grade connectors pre-installed
• Split-loom protective braid covering the wiring
• Detailed installation instructions

Ideal For:

This harness is ideal for automotive enthusiasts, professional tuners, and engine builders working with Chrysler Gen III HEMI engines from 2003 to 2018. It is especially suited for those upgrading to Holley EFI systems, performing engine swaps, or adding power enhancements such as forced induction or nitrous oxide. The harness provides the necessary wiring infrastructure to unlock advanced fuel and ignition control, enabling precise tuning and improved engine performance.

Holley EFI delivers standalone engine management and EFI systems built for everything from engine swaps to serious horsepower builds. With platforms like Sniper, Terminator X, HP, and Dominator, Holley EFI is aimed at enthusiasts who want modern tuning control, data, and drivability—whether it’s a street car, track car, or full-on race program.