| Parameter | Details |
|---|---|
| Product Name | External Wiring Harness (Boom / Stick / Cab Exterior Harness) |
| Part Number | 291-7590 (also 2917590) 291-7589（also 2917589） |
| Compatible Brands | Caterpillar (CAT) |
| Compatible Excavator Models | CAT 320D, 320D L, 323D |
| Harness Type | External / Boom & Stick Harness (As-Fitted) |
| Material | Copper wire + PVC/TPE insulation + Rubber seals |
| Packing | PP bag inside, carton box outside |
| Payment Terms | Western Union, L/C, T/T, MoneyGram, D/A, D/P |
| MOQ | Acceptable trial order (1 piece accepted) |
| Shipping Mode | Air/Sea/Express (FedEx, UPS, DHL, TNT, etc.) |
| Place of Origin | Guangdong, China |
| Brand Name | COGENG |
| Certification | ISO9001 |
| Stock Status | ✅ In Stock |
| Supply Capacity | 500 PCS |
The COGENG 291-7590 External Harness is a high-quality, direct OEM replacement wiring assembly specifically designed for the Caterpillar 320D, 320D L, and 323D excavators. Unlike the chassis or engine harnesses that reside inside the machine frame or engine bay, the External Harness is the wiring that runs on the outside of the machine—specifically along the boom, stick, and cab roof.
This harness is the lifeline for all electrical functions outside the cab, including:
Boom & Stick Lighting: Work lights illuminating the jobsite.
Rotating Beacon: Safety warning light on the cab roof.
Boom Angle Sensors: For machine stability and Auto-Lift systems.
Attachment Controls: Wiring for hydraulic quick couplers and auxiliary circuits.
Camera Systems: Rearview and boom-tip cameras (if equipped).
Because it is fully exposed to the elements, this harness endures extreme UV radiation, rain, mud, rocks, branches, and constant flexing as the boom and stick move. It is manufactured to OEM specifications using 100% copper conductors (tin-plated for corrosion resistance), UV-resistant PVC insulation, and IP67 waterproof connectors to ensure longevity in the harshest conditions.
Why Choose COGENG 291-7590?
Direct Fit: Matches the exact routing for 320D/323D (fixed and long booms).
Plug-and-Play: Pre-terminated with all connectors—no splicing required.
Durable Construction: Resists oil, diesel, UV, and physical abrasion.
In Stock: Ready for immediate shipment.
| Component | Quantity | Description |
|---|---|---|
| Main External Trunk | 1 | Runs from cab roof down boom, to stick tip. |
| Cab Roof Branch | 1 | Beacon light, mirror heaters, roof lights. |
| Boom Section (Lower) | 1 | Auxiliary wiring (quick coupler, lower boom light). |
| Boom Section (Upper) | 1 | Boom angle sensor, upper boom lights. |
| Stick Section | 1 | Stick lights and stick position sensor. |
| Bucket / Tip Branch | 1 | Bucket light, end-of-stick connectors. |
| Connectors (Varied) | As req'd | Deutsch DT, AMP, Sure-Seal (pre-attached). |
| Cable Ties & Clips | As req'd | Factory-style push mounts and zip ties. |
| Protective Sleeving | Full length | Corrugated loom + braided sleeving at pivot points. |
The External Harness follows the exterior of the excavator from the cab to the bucket.
Section 1: Cab Roof (Cab Exterior)
Routing: Exits the rear of the cab roof.
Components: Rotating beacon, cab roof work lights, mirror heaters.
Protection: Hard plastic corrugated loom.
Section 2: Boom Foot (The Pivot Point)
Routing: Crosses the boom pivot joint. Requires a service loop (extra slack) to allow boom movement without pulling connectors apart.
Connections: Main power feed, quick coupler solenoid, lower boom light.
Section 3: Mid-Boom (The "Knuckle")
Routing: Crosses the boom-stick joint. Heavy-duty nylon braided sleeving protects against chafing at the joint.
Connections: Boom angle sensor, stick position sensor.
Section 4: Stick Section
Routing: Runs along the top or side of the stick.
Components: Stick lights (typically 2), wiring for pin grabber coupler.
Section 5: Bucket / End of Stick
Termination: Ends at the bucket linkage area.
Components: Bucket light (single light), spare connector for hammer/shear attachments.
This harness is specifically designed for the D-Series medium excavators.
| Machine Model | Engine | Compatible Harness | Notes |
|---|---|---|---|
| CAT 320D | C6.6 / C7 | 291-7590 | Standard boom (5.7m) |
| CAT 320D L | C6.6 / C7 | 291-7590 | Long undercarriage – same harness |
| CAT 320D LRR | C6.6 / C7 | 291-7590 | Reduced swing – verify routing |
| CAT 323D | C7 / C7.1 | 291-7590 | Same boom/electrical platform as 320D |
| CAT 323D L | C7 / C7.1 | 291-7590 | Long undercarriage – same harness |
| CAT 320D GC | C6.6 | ⚠️ Verify | Different cab/roof harness configuration |
⚠️ Important: This harness is for external boom/stick wiring. If your machine has a hammer/shear circuit, additional auxiliary harness sections may be required (sold separately).
✅ Direct OEM replacement for:
CAT Part Number: 291-7590
CAT Part Number: 2917590 (no dash)
✅ Designed For:
CAT 320D (Standard and L variants)
CAT 320D L (Long Undercarriage)
CAT 323D (Standard and L variants)
CAT 320D LRR (Reduced Radius)
✅ Fits the Following Boom/Stick Combinations:
Standard Boom (5.7m) + Standard Stick (2.9m)
Standard Boom (5.7m) + Long Stick (3.7m)
Heavy-Duty Boom (6.0m) + Stick (3.2m) – verify length
⚠️ Critical Verification Checks:
Boom Length: 291-7590 is for standard/reach booms (5.7m–6.0m). For the 320D Mass Excavation boom (shorter, thicker), a different harness (typically 291-7589) is required.
Sensor Configuration: Some 323D machines have an additional boom angle sensor (Tier 4 emissions). Verify your old harness has the same number of connectors.
Quick Coupler: Confirm whether your machine has a manual or hydraulic coupler. The harness includes the wiring for hydraulic couplers.
❌ NOT Compatible With:
CAT 320D with Mass Excavation boom (shorter boom – harness will be too long).
CAT 320C or 320B (older 12V systems, different connector styles).
CAT 324D / 325D / 329D (longer booms – harness too short).
CAT 320E / 323E (different roof light layout and CAN bus architecture).
R-Series excavators.
Step 1: Preparation
Fully lower boom and stick to the ground.
Disconnect both batteries (negative first).
Open the cab roof panel and rear access doors.
Step 2: Removing the Old Harness
Label everything. There are usually 6-8 connectors along the boom.
Disconnect the main bulkhead connector (usually behind the cab roof, near the beacon).
Carefully trace the harness down the boom. Do not cut – the harness is clipped to the boom with plastic push-mounts. Use a flathead screwdriver to pop them open.
At the boom-stick joint, disconnect the stick section.
Remove the old harness and lay it on the ground for reference (length check).
Step 3: Installing the New Harness
Start from the Cab Roof and work towards the stick tip.
Service Loops: When crossing the boom pivot and the boom-stick pivot, ensure you leave a "droop loop" of about 20-30cm. This allows the joint to articulate without pulling the connectors tight.
Clips: Use the provided OEM-style push clips. Do not over-tighten zip ties around the harness – it can crush the wires.
Step 4: Final Checks & Testing
Do not fully tighten the harness until the boom has been raised and lowered once to check for pulling.
Reconnect batteries.
Turn the key to "ON" (do not start).
Test all functions: Beacon, Boom Lights, Stick Lights, Quick Coupler (engage/disengage), and Camera (if equipped).
Q1: What is the difference between the External Harness (291-7590) and the Cab/Chassis Harness?
A: The External Harness is outside the machine (boom/stick). The Chassis Harness is inside the frame (engine bay). The Cab Harness is inside the cab. They connect via a bulkhead connector at the cab roof.
Q2: How do I know if I need 291-7590 or another harness for my 320D?
A: If your boom is a standard reach boom (longer, thinner), you need 291-7590. If your boom is a Mass Excavation boom (shorter, thicker), you likely need 291-7589 (similar but shorter length).
Q3: My beacon stopped working – do I need the whole harness?
A: Often no. If only one light fails, it’s likely just the bulb or a localized chafe. We recommend replacing the whole harness if you see multiple cracks in the outer insulation or if water has corroded the connectors at the pivot points.
Q4: Does this harness support the hydraulic quick coupler?
A: Yes. The 291-7590 includes the pre-wired connector for the standard CAT hydraulic quick coupler. If your machine has a pin-grabber type, this harness still carries the pilot signal.
Q5: Is this a genuine CAT part?
A: No. COGENG is an aftermarket manufacturer (ISO9001) . Our parts are built to OEM specifications.
Ordering Information
✅ In Stock – Ready to Ship.
✅ MOQ 1 piece accepted for trial orders.
📞 Contact COGENG supplier today to place your order!
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