Diagnosing Electrical Failure in the Upright MX19 Scissor Lift

[MikePhua]

The Upright MX19 and Its Design Legacy
The Upright MX19 is a compact electric scissor lift originally manufactured by Upright Inc., a company later absorbed into Snorkel International. Designed for indoor maintenance, warehouse access, and light construction, the MX19 features a narrow chassis, platform heights up to 19 feet, and a battery-powered drive system. Its popularity stemmed from simplicity, maneuverability, and ease of service. Though production ceased years ago, thousands remain in use globally, especially in rental fleets and small facilities.
The MX19’s electrical system is built around a 24V DC architecture powered by deep-cycle batteries. Control signals are routed through relays, contactors, and joystick inputs, with safety interlocks and emergency stop functions integrated into the upper and lower control panels.
Terminology and Component Notes
- Contactor: A high-current relay used to switch power to the drive or lift motors.
- White Rodgers 586-314111: A common solenoid contactor used in MX19 lifts, responsible for energizing motor circuits.
- Ground Reference: A shared electrical return path essential for stable voltage and signal integrity.
- Stop Button: A safety interlock that disables power when depressed, often located on the upper control panel.
- Green Corrosion: Oxidation of copper conductors, often indicating moisture intrusion and electrical resistance.
Symptoms and Intermittent Behavior
In one case, an MX19 that had sat outdoors for an extended period began exhibiting erratic electrical behavior. The onboard charger failed, prompting the use of external automotive chargers. Initially, the lift operated normally, but after increased daily use, it began to fail intermittently. When the stop button was released, the contactor clicked repeatedly but the lift did not respond. After sitting idle for hours or overnight, the lift would sometimes resume operation briefly before failing again.
This pattern suggests a combination of corroded connections, unstable grounding, and possibly a failing contactor coil or control circuit.
Diagnostic Strategy and Field Observations
The first step in troubleshooting is verifying battery health and voltage. New batteries had been installed and fully charged, ruling out low voltage as the primary cause. Attention then shifted to the contactor and associated wiring.
Recommendations:

• Inspect all battery cables for signs of green corrosion, especially near terminals and crimp points
  
• Replace any cables showing internal oxidation, as resistance can propagate through the conductor
  
• Clean all ground connections and verify continuity between chassis ground and control panel ground
  
• Test voltage at the contactor terminals during activation; power should appear on the load side when the coil is energized
  
• Bypass the contactor temporarily to test motor response directly
  

One technician noted that green corrosion is often terminal for copper cables. Once oxidation enters the strands, cleaning the ends is insufficient. Full cable replacement is the only reliable solution.
Contactor Behavior and Control Circuit Integrity
The White Rodgers contactor clicking without motor response suggests that the coil is receiving signal, but the internal contacts may be pitted or stuck. Alternatively, the control signal may be unstable due to poor grounding or intermittent switch contact.
To test the contactor:

• Measure voltage across the coil when the stop button is released
  
• Check for voltage drop across the main terminals when energized
  
• Listen for solid engagement rather than rapid clicking
  
• Inspect the coil for heat damage or discoloration
  

If the contactor fails to pass current despite audible clicking, replacement is recommended. These units are widely available and relatively inexpensive.
Charger Replacement and System Restoration
The failed onboard charger should be replaced with a unit rated for 24V battery banks and capable of delivering at least 15–20 amps. Smart chargers with float and equalization modes are preferred to extend battery life.
Suggestions:

• Use a charger with automatic shutoff and temperature compensation
  
• Mount the charger in a dry, ventilated location to prevent future failure
  
• Verify that the charger output matches battery chemistry (flooded lead-acid vs AGM)
  

In one retrofit, a technician installed a NOCO Genius charger with onboard diagnostics and Bluetooth monitoring, allowing remote status checks and fault alerts.
Preventative Maintenance and Long-Term Reliability
To maintain electrical integrity in older MX19 lifts:

• Inspect and clean all terminals quarterly
  
• Replace corroded connectors with sealed, heat-shrink terminals
  
• Apply dielectric grease to exposed contacts
  
• Store the lift indoors or under cover to prevent moisture intrusion
  
• Exercise the lift weekly to prevent contact oxidation and mechanical binding
  

For units in daily use, consider installing a battery monitor to track voltage and charge cycles. This helps identify failing batteries before they compromise system performance.
Conclusion
Electrical issues in the Upright MX19 often stem from corrosion, grounding faults, and aging components. With methodical diagnostics and targeted replacements—especially of cables and contactors—these lifts can be restored to reliable service. In compact access equipment, every wire matters, and even a single green strand can bring the whole system down. But with patience and precision, the MX19 proves that even rusted iron can rise again.