JLG 26MRT Scissor Lift Diagnostics Electrical Faults and Drive System Recovery

[MikePhua]

The 26MRT and JLG’s Mid-Range Scissor Lift Lineage
The JLG 26MRT is part of JLG’s MRT series of rough terrain scissor lifts, designed for elevated work in construction zones, maintenance yards, and industrial sites. With a platform height of 26 feet and a working height of over 32 feet, the 26MRT offers a wide deck, four-wheel drive, and a robust hydraulic system for lifting and travel. Its design emphasizes stability, simplicity, and serviceability, making it a popular choice for contractors operating on uneven surfaces.
JLG Industries, founded in 1969, has become a global leader in aerial work platforms. The MRT series was developed to bridge the gap between slab scissor lifts and full-size boom lifts, offering off-road capability without sacrificing compactness. The 26MRT is powered by a gas or diesel engine driving hydraulic pumps, with electrical controls managing lift, drive, and safety interlocks.
Terminology Annotation:

• Scissor Lift: A vertical aerial platform that raises via crisscrossing supports.
  
• Rough Terrain: Equipment designed to operate on uneven or unpaved surfaces.
  
• Safety Interlock: A system that prevents certain functions unless conditions are met, such as platform stowed or outriggers deployed.
  

Common Electrical and Drive System Faults
Operators may encounter issues such as:

• Lift or drive functions not responding
  
• Platform controls dead or intermittent
  
• Warning lights flashing without clear fault codes
  
• Audible clicks from relays but no movement
  
• Drive motors engaging briefly then cutting out
  

These symptoms often point to:

• Faulty limit switches or misaligned sensors
  
• Corroded connectors in the control box or chassis harness
  
• Weak battery voltage affecting solenoid activation
  
• Failed drive motor contactors or hydraulic valve coils
  
• Ground faults or broken wires in the joystick circuit
  

In one construction site in Alberta, a 26MRT refused to drive forward despite full battery and engine operation. After tracing the wiring, technicians found a broken ground wire near the rear axle. Reconnecting the wire restored full function instantly.
Control Box and Relay Diagnostics
The control box on the platform contains the joystick, toggle switches, and diagnostic LEDs. It communicates with the main control board via a multi-pin harness. When functions fail, the issue may lie in:

• Loose or corroded pins in the connector
  
• Worn joystick potentiometer
  
• Failed relay on the main board
  
• Blown fuse in the lower control panel
  

Diagnostic steps:

• Check voltage at the joystick output (typically 0–5V range)
  
• Inspect relays for heat damage or clicking without continuity
  
• Test fuses with a multimeter rather than visual inspection
  
• Wiggle connectors while monitoring function to detect intermittent faults
  

Terminology Annotation:

• Potentiometer: A variable resistor used to measure joystick position.
  
• Continuity: A complete electrical path; lack of continuity indicates a break.
  
• Multimeter: A tool used to measure voltage, resistance, and continuity.
  

In one rental fleet in Florida, repeated drive failures were traced to a cracked relay socket. After replacing the socket and relay, the lift operated reliably across multiple jobs.
Hydraulic Drive and Lift System Checks
The 26MRT uses hydraulic motors for drive and cylinders for lift. If electrical signals are present but movement is absent, the issue may be hydraulic:

• Low fluid level or contaminated oil
  
• Stuck valve spool in the directional control block
  
• Weak solenoid coil unable to shift the valve
  
• Pressure relief valve misadjusted or leaking
  

Recommendations:

• Check hydraulic fluid level and color (should be clear amber)
  
• Tap valve body gently to free stuck spools
  
• Measure coil resistance (typically 8–12 ohms)
  
• Inspect for leaks around fittings and hoses
  

Terminology Annotation:

• Directional Control Valve: A valve that routes hydraulic fluid to different actuators based on input.
  
• Solenoid Coil: An electromagnetic device that moves the valve spool when energized.
  
• Relief Valve: A safety valve that limits system pressure to prevent damage.
  

In one industrial yard in Oregon, a lift cylinder failed to extend. The cause was a blocked filter restricting flow. After replacing the filter and flushing the system, lift speed returned to normal.
Battery and Charging System Maintenance
Even on engine-powered models, the 26MRT relies on batteries to energize control circuits. Weak or sulfated batteries can cause erratic behavior, especially in cold weather.
Maintenance tips:

• Use deep-cycle batteries rated for industrial use
  
• Clean terminals monthly and apply dielectric grease
  
• Test voltage under load (should remain above 11.5V)
  
• Replace batteries every 3–4 years or when capacity drops
  

Terminology Annotation:

• Deep-Cycle Battery: A battery designed for sustained discharge and recharge cycles.
  
• Sulfation: The buildup of lead sulfate crystals that reduce battery capacity.
  
• Dielectric Grease: A non-conductive lubricant that prevents corrosion on electrical contacts.
  

In one municipal fleet in Michigan, battery failure caused intermittent lift lockouts. After switching to AGM batteries and installing a smart charger, reliability improved dramatically.
Preventative Measures and Operator Awareness
To reduce faults and downtime:

• Perform weekly function tests and visual inspections
  
• Train operators to recognize early signs of electrical failure
  
• Keep control boxes dry and protected from impact
  
• Document fault codes and repair actions for future reference
  

In one airport maintenance crew in Texas, implementing a pre-shift checklist reduced lift failures by 80% and improved technician response time.
Conclusion
The JLG 26MRT is a capable rough terrain scissor lift—but its performance depends on clean electrical signals, responsive hydraulics, and healthy batteries. When faults arise, methodical diagnosis and preventative care restore function and extend service life. In elevated work, reliability begins on the ground—and the 26MRT proves that with the right attention, even complex systems can stay simple.