Electrical Issues in John Deere 750B Dozers

[MikePhua]

Electrical issues are a common but often challenging problem for heavy machinery operators and technicians. The John Deere 750B, a track-type tractor (dozer), is a prime example of a machine where electrical problems can arise, impacting performance and efficiency. These issues can stem from a range of causes, including faulty wiring, malfunctioning components, or improper maintenance. This article provides an in-depth look into how to diagnose and resolve electrical issues in a John Deere 750B dozer.
Understanding the John Deere 750B Dozer
The John Deere 750B is a popular dozer model known for its robust construction and versatility. Manufactured in the late 1980s and early 1990s, it is equipped with a diesel engine capable of producing around 100 horsepower. This machine is often used in construction, land clearing, and mining operations. Like most older heavy machinery, the 750B can experience electrical issues as the machine ages and components wear out.
Common Electrical Issues in John Deere 750B
Electrical problems in the John Deere 750B can manifest in various ways. The key is to pinpoint the source of the issue to restore the machine's functionality. Some of the most common electrical issues include:
1. Battery and Charging System Issues

• Symptoms: The most apparent issue with the battery or charging system is that the dozer may fail to start, or it may start intermittently. If the battery is not charging properly, you might notice dim lights or difficulty starting the engine, especially after the machine has been idle for some time.
  
• Possible Causes:
  • Faulty alternator: The alternator is responsible for charging the battery while the engine runs. If it fails, the battery will eventually drain.
    
  • Corroded battery terminals: Dirt, rust, and corrosion can cause poor connections, leading to low voltage supply to the starter motor or other components.
    
  • Damaged wiring: Over time, the wiring in the charging system can degrade, particularly if exposed to harsh weather conditions or friction.
    
• Diagnosis and Solution:
  • Test the alternator: Use a voltmeter to check the alternator’s output voltage. A healthy alternator should produce a voltage between 13.5 to 14.5 volts.
    
  • Clean battery terminals: Ensure that the battery terminals are clean and free of corrosion. Use a wire brush to remove any buildup of rust.
    
  • Check for continuity: Use a multimeter to check for continuity in the charging circuit wiring. If the wiring is faulty, replace or repair it.
    

2. Starter Motor Problems

• Symptoms: A faulty starter motor can prevent the engine from starting altogether. If you hear a clicking noise when turning the ignition but the engine doesn't turn over, the starter motor might be the culprit.
  
• Possible Causes:
  • Worn-out starter solenoid: The solenoid is responsible for engaging the starter motor. If it fails, the motor won't engage properly.
    
  • Faulty wiring or connections: Loose or corroded connections can cause a weak or inconsistent signal to the starter motor, preventing it from functioning correctly.
    
• Diagnosis and Solution:
  • Test the solenoid: If the starter motor is not engaging, test the solenoid by applying direct voltage to it. If it fails to operate, replace the solenoid.
    
  • Check wiring and connections: Ensure all wiring to the starter motor is intact, clean, and properly connected.
    

3. Electrical Short Circuits

• Symptoms: Electrical shorts can cause various problems in the dozer, from blown fuses to malfunctioning lights, gauges, and controls. Short circuits often lead to a complete loss of power to certain systems.
  
• Possible Causes:
  • Damaged wiring: Worn or frayed wires can cause short circuits when they come into contact with other metal surfaces or each other.
    
  • Faulty components: Components such as the ignition switch, relay, or fuse can malfunction and cause electrical shorts.
    
• Diagnosis and Solution:
  • Inspect wiring: Check for damaged, exposed, or frayed wires, especially in high-traffic areas like around the engine bay or under the dashboard.
    
  • Use a multimeter: To locate a short, use a multimeter to test continuity between the electrical components and check for any irregular resistance that might indicate a short.
    

4. Faulty Electrical Relays and Fuses

• Symptoms: If a relay or fuse fails, you may notice that certain electrical functions (such as lights, the fan, or the hydraulic system) stop working. Often, the issue will be localized to one specific system.
  
• Possible Causes:
  • Blown fuses: Overloaded circuits or short circuits can cause fuses to blow. This is usually an easy fix by replacing the blown fuse.
    
  • Bad relay: The relays control the flow of electrical current to various components. A faulty relay can prevent proper operation of the electrical system.
    
• Diagnosis and Solution:
  • Check fuses and relays: Inspect the fuses and relays for any visible signs of damage or wear. Replace any blown fuses or faulty relays.
    
  • Use a multimeter to test relays: You can test relays by measuring the voltage at the terminals to ensure proper function.
    

5. Instrument Cluster Malfunctions

• Symptoms: The instrument cluster is vital for providing the operator with information such as engine temperature, fuel levels, and pressure gauges. If the cluster starts to show erratic readings or goes completely dark, it may indicate an electrical problem.
  
• Possible Causes:
  • Faulty wiring or connections: Poor connections between the instrument cluster and the main electrical system can cause inaccurate readings.
    
  • Blown fuses or damaged gauges: A blown fuse can prevent certain readings from being displayed, and a damaged gauge may need replacing.
    
• Diagnosis and Solution:
  • Inspect the wiring: Check all wiring leading to the instrument cluster for damage or corrosion.
    
  • Replace damaged gauges: If a specific gauge is malfunctioning, it may need to be replaced or recalibrated.
    

Preventive Maintenance for Electrical Systems
Electrical issues in older dozers like the John Deere 750B are often a result of neglect or poor maintenance. To prevent electrical problems from arising, follow these key maintenance steps:

1. Regular Inspections: Periodically inspect the battery, wiring, and all electrical components for signs of wear, corrosion, or damage.
   
2. Keep Connections Clean: Ensure that all connections, especially the battery terminals, are clean and free from corrosion.
   
3. Monitor Battery Voltage: Regularly check the battery voltage to ensure the charging system is working as expected.
   
4. Replace Worn Components: Don’t wait for electrical problems to become severe. Replace damaged or worn components as needed.
   

Conclusion
Electrical issues in the John Deere 750B can be a frustrating experience, but with the right approach, these problems can be diagnosed and repaired effectively. Whether it’s dealing with the charging system, starter motor, electrical shorts, or instrument cluster malfunctions, understanding the root causes and following a systematic troubleshooting process is key. Regular maintenance and timely repairs will ensure that the John Deere 750B continues to perform at its best, reducing downtime and maximizing productivity on the job site.