Mastering Wiper Motor Wiring on the CAT 140H Motor Grader

[MikePhua]

Overview of the Wiper Motor and Its Wiring Context

• The wiper motor assembly on the CAT 140H includes the motor and linkage mechanisms that convert its rotation into sweeping motion for the windshield wipers .
  
• On motor graders like the 140H, there are separate circuits for front lower, front upper, and possibly rear wiper motors, each tied to specific connector pins .
  

Wiring Pin Configuration & Testing Notes

• In analogous CAT machinery, a common wiring practice uses Green (light green/green) for power delivery to pin 1 of the wiper motor and Brown (brown/light-green) for the return or ground path at another pin .
  
• The testing procedure is straightforward: apply 12 V to the green (power) wire and ground to the brown (return) wire. If the motor runs, it’s functional—if not, replacement is likely needed .
  

Electrical Connector Locations on the 140H

• The standard schematic reveals the following component-connector mappings:
  • Front Lower Wiper Motor: Connector at location C‑4.
    
  • Front Upper Wiper Motor: Connector at location D‑4.
    
  • Rear Wiper Motor: Connector at location B‑11 (if equipped) .
    
• Wiring diagrams provide pin-out tables showing circuits by number, color, and function—valuable for precise diagnostics .
  

Terminology & Technical Notes

• Connector Location (e.g., C‑4, D‑4, B‑11): Indicates where the component connects within the machine’s harness.
  
• Light Green / Green (RLG) Wire: Typically supplies battery power to the wiper motor’s main input.
  
• Brown / Light Green (NLG) Wire: Typically serves as the ground or return path.
  
• Pin Testing: Applying power to pin 1 (Green) and grounding the NLG wire helps determine motor functionality.
  
• Multi-Motor Configuration: Separate wiring runs for lower, upper, and rear wipers require precise component matching during troubleshooting.
  

Real-World Scenario: Diagnosing a Non-Working Wiper

• An operator experiences intermittent wiper operation on the front window of a CAT grader. The wiper stops partway or doesn’t function consistently.
  
• Using a multimeter, they confirm 12 V is present on the green power wire at the C‑4 connector. Grounding the brown wire manually activates the motor, confirming the motor itself is good.
  
• The real culprit turns out to be a faulty switch or a loose grounding point—once repaired, the wipers operate smoothly again.
  

Summary of Key Takeaways

• CAT 140H motor graders use distinct circuits for each wiper motor—identify connector (C‑4, D‑4, B‑11) before troubleshooting.
  
• Power typically flows via a green-colored wire to pin 1; grounding often occurs through a brown/light-green wire.
  
• Direct testing can distinguish between a bad motor and wiring or switch issues.
  
• Accurate wiring diagrams (with pin number, color, and connector location) are essential tools for effective diagnostics.