Takeuchi TB135 Electrical Shutdown Fault and Stuck-On Ignition

[MikePhua]

The TB135 and Its Electrical Simplicity
The Takeuchi TB135 is a compact excavator introduced in the early 2000s, designed for tight-access excavation, utility trenching, and light demolition. With an operating weight around 7,000 lbs and a digging depth of nearly 11 feet, it became popular for its mechanical reliability and straightforward hydraulic layout. One of its defining traits is its relatively simple electrical system—an advantage for field repairs but also a vulnerability when components age or wiring degrades.
The ignition system in the TB135 is a basic keyed switch that energizes the fuel solenoid, starter relay, and accessory circuits. When functioning properly, turning the key to OFF cuts power to the fuel shut-off solenoid, stopping the engine. However, when the machine remains running after the key is turned off, or the ignition stays energized without input, the issue is almost always electrical.
Symptoms of a Stuck-On Ignition Circuit
Operators may encounter:

• Engine continues running after key is turned off
  
• Ignition lights remain on with key removed
  
• Starter relay clicks intermittently when machine is off
  
• Battery drains overnight despite no usage
  
• Fuel solenoid remains energized continuously
  
• Key switch feels loose or unresponsive
  

A contractor in British Columbia reported that his TB135 wouldn’t shut off even after disconnecting the key switch. The engine only stopped after manually cutting power at the battery, confirming a stuck-on circuit.
Root Causes and Diagnostic Pathways
Common causes include:

• Faulty ignition switch with internal short
  
• Stuck relay in the starter or fuel solenoid circuit
  
• Ground loop or backfeed from accessory wiring
  
• Corroded connectors causing unintended continuity
  
• Worn insulation allowing wires to arc or fuse together
  
• Bypass wiring from previous repairs creating feedback
  

To diagnose:

• Disconnect the ignition switch and test continuity across terminals
  
• Inspect relays for heat damage or stuck contacts
  
• Use a multimeter to trace voltage from battery to solenoid
  
• Check for voltage at the fuel solenoid with key OFF
  
• Inspect wiring harness for melted or pinched sections
  
• Test ground integrity at the frame and battery
  

A technician in Georgia found that a previous owner had bypassed the ignition switch with a toggle hidden under the dash. The toggle had failed in the ON position, keeping the solenoid energized even when the key was removed.
Repair Strategies and Component Access
Once the fault is identified, repairs may include:

• Replacing the ignition switch with OEM or marine-grade sealed unit
  
• Installing new relays with proper amperage rating
  
• Rewiring damaged sections with heat-shrink connectors
  
• Adding a master disconnect switch to isolate battery during storage
  
• Cleaning all ground points and applying dielectric grease
  
• Labeling accessory wires to prevent future confusion
  

Recommended tools:

• Multimeter with continuity and voltage test modes
  
• Wire strippers and crimpers
  
• Relay tester or jumper leads
  
• Schematic diagram for TB135 electrical system
  
• Flashlight and inspection mirror for tight compartments
  

A fleet manager in Texas rebuilt the ignition circuit on three TB135 units using marine-grade switches and sealed relays, eliminating shutdown issues and improving reliability in wet conditions.
Preventive Measures and Long-Term Reliability
To avoid future electrical faults:

• Inspect wiring harness quarterly for abrasion or heat damage
  
• Replace ignition switches every 2,000 hours or when wear is evident
  
• Use sealed connectors in high-moisture environments
  
• Avoid splicing wires without proper connectors and insulation
  
• Train operators to report unusual electrical behavior early
  
• Keep a wiring diagram onboard for field diagnostics
  

A landscaping crew in Maine added a checklist to their daily startup routine, including ignition switch feel and solenoid response. This helped catch a failing relay before it stranded the machine on a remote jobsite.
Conclusion
Electrical faults in the Takeuchi TB135 are often simple in nature but disruptive in the field. A stuck-on ignition circuit can drain batteries, confuse operators, and compromise safety. With methodical diagnostics, clean wiring practices, and quality components, these issues can be resolved and prevented. In compact excavators, reliability isn’t just mechanical—it’s wired into every start and stop.