Locating and Troubleshooting the Starter Relay on the John Deere 35D

[MikePhua]

The John Deere 35D and Its Compact Excavator Lineage
The John Deere 35D mini excavator was introduced in the mid-2000s as part of Deere’s D-series compact equipment. Designed for tight job sites and utility work, the 35D features a zero tail swing design, a 3.5-ton operating weight, and a Yanmar diesel engine. Its compact footprint and hydraulic precision made it a popular choice among landscapers, contractors, and municipalities.
John Deere, founded in 1837, has long been a leader in agricultural and construction machinery. The D-series marked a shift toward improved operator comfort, electronic diagnostics, and simplified maintenance. However, like many compact machines, electrical issues—especially related to starting—can be frustrating to diagnose.
Terminology Notes

• Starter Relay: An electrical switch that controls the high-current flow to the starter motor, triggered by the ignition key.
  
• Solenoid: A coil-based actuator that engages the starter gear with the engine flywheel.
  
• ECU (Engine Control Unit): The onboard computer that manages engine functions and safety interlocks.
  
• Fuse Block: A panel containing fuses and relays, typically located under the operator seat or behind a service panel.
  

Starter Relay Location and Access Strategy
On the John Deere 35D, the starter relay is typically located within the main fuse block, which is mounted behind the right-side access panel near the operator’s seat. To access it:

• Open the right-side engine compartment panel
  
• Locate the fuse block mounted vertically near the battery tray
  
• Identify the relay labeled “START” or “IGNITION” depending on the year
  
• Use a test light or multimeter to verify voltage during key-on
  

In some units, the relay may be mounted separately near the starter motor itself, especially if the machine has undergone electrical modifications or field repairs. Always trace the wiring harness from the ignition switch to confirm relay placement.
A technician in British Columbia once spent hours chasing a no-crank issue on a 35D, only to find that the starter relay had been relocated during a previous repair and zip-tied near the hydraulic pump. After restoring it to the fuse block and replacing the corroded terminals, the machine started reliably.
Symptoms of Relay Failure and Diagnostic Tips
When the starter relay fails or loses connection, the machine may exhibit:

• No crank when turning the key
  
• A single click from the solenoid with no engine turnover
  
• Intermittent starting depending on temperature or vibration
  
• No voltage at the starter motor during key-on
  

Diagnostic steps include:

• Testing voltage at the relay input and output terminals
  
• Listening for relay click when the key is turned
  
• Jumping the relay terminals to bypass and test starter function
  
• Inspecting relay socket for corrosion or loose pins
  

A contractor in Texas reported that his 35D would only start after tapping the fuse block. The relay socket had developed a hairline crack, causing intermittent contact. Replacing the socket and relay resolved the issue permanently.
Preventive Maintenance and Electrical Reliability
To avoid future starter relay issues:

• Clean all electrical connectors annually and apply dielectric grease
  
• Replace relays every 2,000 hours or when symptoms appear
  
• Inspect wiring harnesses for abrasion and heat damage
  
• Use sealed relays in wet or dusty environments
  
• Keep battery terminals tight and corrosion-free
  

A fleet manager in Ohio implemented a quarterly electrical inspection protocol for all compact excavators. Over two years, starter-related downtime dropped by 70%, and repair costs were reduced significantly.
Real-World Anecdotes and Lessons Learned
In 2022, a landscaping crew in Vermont faced repeated no-start conditions on their 35D. After replacing the battery and starter motor, the issue persisted. A field technician traced the fault to a relay that had overheated due to a loose ground. After installing a new relay and rerouting the ground wire, the machine started instantly and ran without issue.
Another story from Australia involved a 35D that wouldn’t start after a rainstorm. Moisture had entered the fuse block through a cracked panel seal. The starter relay was corroded internally. After replacing the relay and sealing the panel with silicone, the machine returned to service.
Final Thoughts
The starter relay on the John Deere 35D may be a small component, but its failure can halt operations entirely. Knowing its location, understanding its function, and applying methodical diagnostics are essential for keeping the machine reliable. With proper care and attention to electrical integrity, the 35D remains a dependable tool for compact excavation tasks across diverse job sites. For operators and technicians alike, mastering the electrical system is key to minimizing downtime and maximizing productivity.