EFI Main Power Harness

The Holley EFI Main Power Harness (HLY558-308) is the backbone of any Holley Dominator EFI fuel injection system installation. Built for serious engine builders and restoration shops, this main power harness handles the critical electrical pathway between your vehicle's battery, alternator, and the Dominator EFI ECU. Without a properly engineered main harness, even the most sophisticated fuel injection system cannot function reliably—making this component non-negotiable for anyone converting a classic carbureted engine to modern EFI or upgrading an existing electronic fuel injection setup.

This harness is engineered with precision-crimped terminals and heavy-gauge primary wiring designed to handle peak amperage demands during engine startup and full-load operation. The main power harness manages voltage distribution under dynamic conditions, protecting sensitive ECU circuits from electrical noise and ensuring stable fuel delivery at all RPM ranges. Unlike aftermarket harnesses that skimp on conductor gauge or connector quality, Holley's OEM-grade design incorporates shielding and proper strain relief to withstand underhood vibration and heat exposure—critical factors that directly impact fuel injector response time and ignition timing accuracy.

Technicians and engine builders working on LS swaps, small-block restorations, or late-model engine conversions depend on this harness to establish the electrical foundation before tuning begins. Installation requires careful routing away from exhaust manifolds and moving engine components to prevent degradation of insulation. The compact footprint (10.6 x 3.8 x 11.3 inches) accommodates tight engine bays while the 1.7 lb weight keeps parasitic load minimal. Compatibility with Holley Dominator EFI systems makes this harness essential for builders pursuing consistent fuel metering, precise load compensation, and repeatable wide-range tuning capability.