Cummins 3966805 — Genuine Fuel Injector Wiring Harness for ISB 5.9L

MPN: 3966805  |  Also Known As: injector sub-harness, fuel injection harness  |  Replaces/Predecessors (ID only): 3957309, 3964316  |  OEM Cross-Refs (ID only): 05139865AA, 05086965AA

Genuine Cummins injector wiring harness that restores reliable electrical connections to your common-rail injectors. Direct-fit for 2003–2005 Ram 5.9L ISB. Sold individually; 3 required per engine (one harness per injector pair).

Features & Benefits

• OE connectors & terminals for proper sealing and signal integrity.
• Heat- and oil-resistant jacketing for long service life under the valve cover.
• Direct-fit geometry for clean routing and reduced chafe risk.
• Restores stable injector control to address intermittent misfires caused by brittle/aged wiring.
• Backed by Cummins quality for fit, function, and durability.

Verified Fitment (Automotive)

Industrial/Off-Highway: Used primarily on Tier 3 ISB/QSB 6.7 platforms in certain applications—verify by ESN before ordering.

Specifications

• Type: Fuel injector wiring sub-harness (pair-lead)
• OE Part Number: 3966805
• Predecessor P/Ns (ID only): 3957309, 3964316
• OEM Cross-Refs (ID only): 05139865AA, 05086965AA
• Quantity Required: 3 per engine (sold individually)

Often Paired With

• Injector harness retaining clip: 3963736
• Valve cover gasket (’03–’05): 3954324
• Rocker box gasket: 3963379 (’03–’18 5.9L/6.7L)

What’s In The Box

• (1) Genuine Cummins Injector Wiring Harness (3966805)

Installation Tips

• Disconnect batteries; remove valve cover and inspect routing for chafe points.
• Seat connectors fully until tactile/audible engagement; secure with new retaining clips where needed.
• Verify continuity and avoid sharp bends; re-torque valve cover to spec.

FAQ

HOW MANY HARNESS PIECES DO I NEED?

Three (3) per engine—each sub-harness serves a pair of injectors.

WHAT YEARS DOES 3966805 FIT?

Automotive drop-in for 2003–2005 Ram 5.9L ISB common-rail (verify by VIN/ESN).

WILL THIS WORK ON 2006–2007 5.9L?

Harnessing changed in later years—confirm the correct part number for 2006–2007 before ordering.

IS THIS A GENUINE CUMMINS PART?

Yes—OE Cummins 3966805 for proper connector fit and durability.

DOES IT INCLUDE RETAINING CLIPS OR GASKETS?

No—order clips (3963736) and any needed gaskets (3954324 valve cover, 3963379 rocker box) separately.