Product Description
The CUMMINS 3966805 OEM FUEL INJECTOR WIRING HARNESS is the factory-correct under-valve-cover injector wiring harness for 2003–2005 5.9L ISB Cummins engines. If your Ram is experiencing intermittent misfires, rough running, dead injectors, or electrical-related contribution balance codes, this genuine Cummins harness restores proper electrical delivery to all six common-rail injectors.
Cheap aftermarket harnesses are known for poor crimp quality, heat-related failure, and signal loss. This genuine Cummins 3966805 injector harness ensures OE-level conductivity, correct plug indexing, and long-term resistance to oil contamination—critical for the harsh under-valve-cover environment of the ISB platform.
Key Features & Benefits
- Genuine Cummins OEM injector harness – NOT aftermarket.
- Correct plug orientation and conductor resistance for the ISB 5.9.
- Restores proper injector firing and eliminates signal loss or random misfires.
- Built to withstand valve cover heat, oil vapor, and vibration.
- Direct-fit replacement for 2003–2005 5.9L common-rail Cummins engines.
Fitment
Direct-fit for the following vehicles:
- 2003–2005 Dodge Ram 2500 5.9L Cummins
- 2003–2005 Dodge Ram 3500 5.9L Cummins
Engine Platform: ISB 5.9L 24-valve common-rail
Location: Under valve cover / injector electrical harness assembly
Notes: 2004.5–2005 trucks may require VIN verification due to mid-year electrical changes.
Cross-Reference (ID ONLY)
- Cummins 3966805 (primary part number)
- Mopar reference: 5086877AA
Cross-reference numbers are provided for identification only. Always confirm by VIN or ESN.
Related Genuine Cummins Components (Working CPP Diesel Links)
- CUMMINS 3804899 OEM FRONT CRANKSHAFT SEAL – 5.9L/6.7L CUMMINS
- CUMMINS 3920706 OEM EXPANSION PLUG – TURBO DRAIN – 5.9L/6.7L
- CUMMINS 3937111 FRONT CRANKSHAFT SEAL SERVICE KIT – 5.9L
- CUMMINS 3946495 OEM HARMONIC BALANCER DOWEL PIN – ISB 5.9/6.7
Installation Notes
- Disconnect batteries before servicing injector electrical circuits.
- Inspect connectors for heat damage or oil contamination.
- Always torque valve cover hardware to OEM specifications.
- Clear any stored injector-related DTCs after installation.
Specifications for cummins 3966805
| Specification | Detail |
|---|---|
| Brand | Cummins (Genuine OEM) |
| Part Number | 3966805 |
| Component Type | Fuel Injector Wiring Harness (Under Valve Cover) |
| Engine Compatibility | 2003–2005 5.9L ISB Cummins |
| Fuel Type | Diesel |
| GTIN | Not published by Cummins |
| UPC | Not published by Cummins |
| Shipping Weight | Approx. 1 lb |
| Shipping Dimensions | 9 × 5 × 3 in (approx.) |
| Shipping Method | Standard ground / small parcel |
| Cross Reference | Mopar 5086877AA (ID only) |
| E-Codes / Emissions | Not specified (OE electrical component) |
| Prop 65 | This product may expose you to chemicals known to the State of California to cause cancer or reproductive harm. For more information visit P65Warnings.ca.gov. |
FAQ
WILL THIS HARNESS FIX MY INJECTOR MISFIRE ISSUE?
If your misfire is caused by poor electrical continuity under the valve cover, then yes—replacing the harness often resolves dead injectors and random contribution balance codes. Always verify injector health separately.
IS THIS A GENUINE CUMMINS PART?
Yes. CPP Diesel supplies only genuine Cummins 3966805 injector harnesses, not aftermarket copies or offshore substitutes.
DO I NEED TO REMOVE THE VALVE COVER TO INSTALL THIS?
Yes. The harness sits beneath the valve cover and plugs directly into the injector solenoids. Install time is typically 1–2 hours.
SHOULD I REPLACE OTHER PARTS AT THE SAME TIME?
Many owners inspect or replace injector connector seals, and also verify that engine sealing components like the 3804899 front crankshaft seal and 3920706 turbo drain plug are not leaking.
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Product Reviews
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Genuine cummins part
It was a genuine cummins part. The color of wire don't match up to factory for the front injector but I figured it out.
