Solving Electrical Starting Issues on the 1989 Bobcat 743

[MikePhua]

Bobcat 743 Background and Electrical Configuration
The Bobcat 743 skid steer loader was introduced in the mid-1980s as part of Bobcat’s 700-series lineup, designed for compact construction, landscaping, and agricultural tasks. Powered by a Kubota V1702 diesel engine, the 743 featured a straightforward 12-volt electrical system with a mechanical starter solenoid, analog gauges, and minimal electronic controls. Its simplicity made it popular among small contractors and rental fleets, but age-related electrical issues are now common in surviving units.
Terminology Note

• Starter Solenoid: An electromechanical switch that engages the starter motor when the ignition key is turned.
  
• Cranking Voltage: The voltage measured across the battery terminals while the starter is engaged.
  
• Ground Cable: The negative battery cable that completes the electrical circuit through the engine block.
  
• Load Test: A diagnostic procedure that simulates starter draw to evaluate battery health.
  

Symptoms and Initial Diagnosis
A 1989 Bobcat 743 exhibited a classic no-start condition: the starter solenoid clicked but the engine failed to turn over. Bench testing confirmed the solenoid was functional, and 12.4 volts were present at the solenoid terminal. This led to suspicion of a faulty ignition switch, but further investigation revealed deeper issues.
Key observations:

• Solenoid clicked but starter did not engage
  
• Voltage at solenoid was 12.4V at rest
  
• Battery tested fine under static conditions
  
• Cleaning cable ends did not resolve the issue
  

Root Cause and Resolution
The problem was traced to the negative battery cable. Although both ends had been cleaned, internal corrosion or a broken strand within the cable prevented sufficient current flow under load. Replacing the ground cable resolved the issue immediately, allowing the engine to crank and start normally.
This highlights a common misconception: voltage readings alone do not confirm circuit integrity. A cable may pass static voltage but fail under load due to resistance or internal damage.
Diagnostic Strategy and Best Practices

• Always test voltage under load: Use a multimeter while cranking to detect voltage drop.
  
• Inspect ground paths thoroughly: The engine block is the return path for starter current; corrosion here can mimic battery failure.
  
• Replace suspect cables, not just clean them: Internal damage is invisible and often the root cause.
  
• Use a power probe or jumper leads: These tools simplify testing from the operator seat.
  
• Load test the battery: Even a 12.4V reading can mask a shorted cell that collapses under starter draw.
  

In Wisconsin, a technician shared that he once replaced a starter and solenoid on a Bobcat 743 only to discover the real issue was a corroded ground strap hidden behind the engine mount. In Ontario, a Case 1835C owner reported similar symptoms and solved them by replacing both battery cables with marine-grade copper leads.
Preventive Maintenance Recommendations

• Replace battery cables every 5–7 years, especially in high-vibration environments
  
• Use dielectric grease on terminals to prevent corrosion
  
• Check cranking voltage monthly during winter operations
  
• Secure cables with clamps to reduce flex and fatigue
  
• Keep a spare ground cable in the service kit for field repairs
  

Conclusion
Electrical problems on older Bobcat 743 loaders often stem from overlooked components like ground cables. Voltage readings alone can be misleading, and load testing is essential for accurate diagnosis. By replacing aged cables and maintaining clean, tight connections, operators can restore reliable starting and avoid unnecessary parts replacement. The 743’s mechanical simplicity remains its strength—provided its electrical backbone is kept in good shape.