2002–2003 Ford 7.3L Powerstroke Engine Harness F81Z‑12B637‑FA (Federal Emissions Only)

Upgrade the reliability of your late 7.3L Powerstroke with this OE‑style replacement engine wiring harness, built as a direct substitute for Ford part number F81Z‑12B637‑FA. Designed specifically for 2002–2003 Ford F‑250, F‑350, and F‑450 trucks equipped with the 7.3L Powerstroke, federal emissions package, and 4R100 automatic transmission, it replaces the aging factory harness that often suffers from brittle insulation, chafed wires, and corroded connectors after years of heat and vibration.​

This harness is configured for a traditional glow plug relay (federal emissions) and includes factory‑style connectors with correct lengths and routing so it plugs directly into the original sensors, glow plug relay, transmission‑related connections, and engine components with no cutting or splicing. Ideal for solving intermittent no‑start issues, glow plug faults, and random electrical problems tied to failing wiring, it lets you refresh the engine harness on your 7.3/4R100 truck in one clean install instead of chasing individual circuits.

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Key features & benefits

• Direct replacement for Ford OE engine harness part number F81Z‑12B637‑FA

• Fits 2002–2003 Ford F‑250, F‑350, and F‑450 trucks with 7.3L Powerstroke and federal emissions

• Configured for a glow plug relay; not compatible with California trucks that use a glow plug module

• Factory‑style connectors, correct wire lengths, and proper routing for clean, plug‑and‑play installation

• Helps resolve glow plug issues, no‑start, intermittent stalling, and sensor‑related electrical problems linked to damaged wiring

Warranty

This engine harness is backed by a limited 1‑year replacement warranty against defects in materials and workmanship when installed on a correct, stock‑configuration 2002–2003 7.3L Powerstroke federal‑emissions truck matching part number F81Z‑12B637‑FA. The warranty covers failure due to manufacturing defects under normal use; it does not cover damage from improper installation, modification, accidents, misuse, exposure to chemicals, or use on incorrect/emissions‑mismatched applications.

FAQ – 7.3L Federal vs. California Emissions (F81Z‑12B637‑FA)​

Q: How do I know if my 7.3L truck is federal or California emissions?
A: Look at the under‑hood emissions label (usually on the radiator support or underside of the hood). It will state whether the vehicle conforms to “Federal” or “California” emissions regulations.​

Q: Where exactly is the emissions label located?
A: On most 7.3L Super Duty trucks, the emissions label is on the core support in front of the engine bay or on the underside of the hood near the latch area. Wipe it clean to read “federal” vs “California.”​

Q: What is the main difference in the glow plug system?
A: Federal‑emissions 2002–2003 7.3L trucks use a conventional glow plug relay mounted on the passenger side of the engine bay, while California‑emissions trucks use an electronic glow plug control module.​

Q: Why won’t this F81Z‑12B637‑FA harness work on California trucks?
A: The harness is pinned and wired for a glow plug relay, not for the electronic glow plug module used on California‑emissions trucks. The connectors and wiring layout are different, so it will not plug in correctly on California models.​

Q: If I swap to a federal glow plug relay, can I use this harness on a California truck?
A: This is not recommended. California‑emissions trucks are wired and calibrated differently; mixing harnesses, relays, and modules can create electrical and drivability issues and would set a check engine light. Always match the harness to the original emissions configuration.​

Q: What information should I check before ordering this harness?
A: Confirm model year (2002–2003), truck model (F‑250/F‑350/F‑450), engine (7.3L Powerstroke), emissions label (federal only), and OE harness number F81Z‑12B637‑FA on your original part if possible. If you have questions or need help give us a call (888-290-3820) or send us an email.