F81Z-12B637-FA Engine Wiring Harness Compatible with Ford 7.3L - OEM

In this review the F81Z-12B637-FA engine wiring harness is evaluated for owners of 2002-2003 Ford Super Duty trucks and Excursion with the V8 7.3L diesel. The bottom line: this harness is a practical OEM-quality replacement for those who need a complete, plug-and-play wiring assembly that mirrors factory design. It is aimed at technicians or experienced DIYers looking for a direct-fit harness that restores reliable power transmission and keeps the engine electrical system working like the original.

Key Features

• OEM design: Manufactured by an ISO-certified maker to match the functions and specifications of the original harness, reducing fitment confusion during installation.
• Premium copper core: High-quality copper core wires offer lower resistance and improved conductivity for faster, more reliable power transmission.
• Durable insulation: Wrapped plastic surfaces resist high temperatures, chemical reagents and impact to protect circuits under heavy-duty conditions.
• Complete assembly: Comes with all connectors and upgraded integrated power and charge harness for a true plug-and-play replacement.
• Included relays: Supplied with new glow plug and intake heater relays so critical components are renewed with the harness.

Who It's For

The harness is best for owners of 2002-2003 Ford F-250, F-350, F-450, F-550 Super Duty trucks and 2002-2003 Excursion models equipped with the 7.3L diesel, automatic transmission and excluding California emissions. It is suited to professional installers and experienced DIY mechanics who can perform wiring swaps without printed instructions.

Those who should look elsewhere include owners of vehicles with California emissions or non-automatic transmissions, and users who require step-by-step installation guides; professional installation is recommended for reliable results.

Pros & Cons

Pros

• OEM-style construction simplifies replacement and restores original wiring layout.
• High-quality copper cores and reinforced terminals improve electrical reliability under load.
• Complete kit with glow plug and intake heater relays reduces the need to source additional parts.

Cons

• Does not include installation instructions, so less experienced owners may need professional help.
• Not compatible with California emissions models, limiting fitment for some buyers.

Specifications

Part Number	F81Z12B637FA / F81Z-12B637-FA
Compatible Engines	V8 7.3L Diesel
Fitment Years	2002-2003
Compatible Models	F-250, F-350, F-450, F-550, Excursion
Transmission	Automatic only
Included Accessories	Glow plug relays, intake heater relays, all connectors
Emissions	Excludes California emissions

Our Verdict

The F81Z-12B637-FA harness is a sensible, OEM-quality replacement for 2002-2003 Ford 7.3L diesel trucks and Excursion when you need a full, plug-and-play wiring assembly. It offers durable materials, upgraded power wiring and included relays, making it a good value for professionals and experienced DIY installers who need dependable, factory-style fit and performance.

Frequently Asked Questions

Will this harness fit my 2003 F-350 with a 7.3L diesel?
Yes, it is specified for 2002-2003 F-250/F-350/F-450/F-550 Super Duty trucks with the 7.3L diesel and automatic transmission, excluding California emissions.

Does the kit include relays and connectors?
Yes, the assembly includes new glow plug and intake heater relays and all connectors required for the harness as shipped.

Is professional installation required?
Professional installation is recommended since no installation instructions are included and proper wiring procedures are important for reliability.