How an Electric-hydraulic Dump Hoist Works

• The electric-hydraulic unit that does the work of lifting the bed of the dump truck is a complete motor, pump and reservoir in one compact unit. A cable from the vehicle battery is run to the solenoid on the pump unit, and a small gauge wire from the energizing terminal of the solenoid is run to the control switch in the truck cab. Some models have two solenoids, one for up and one for down, and in this instance two wires run to the control switch. Pressing the up or down buttons in the cab energizes the pump solenoid.
  
  

When the Bed Fails to Lift

• When the bed fails to lift, check a few simple things. Determine if the pump is running when the "Up" switch is pressed. A running pump indicates either that the hydraulic fluid level is too low or that the load is too heavy for the pump to lift. It may be necessary to off load some of the cargo to lighten the load to the point where the hoist can lift it or to add hydraulic fluid to the reservoir.
  
  If the pump does not run when the up button is pressed, ensure that there is battery power to the pump solenoid. You can determine this quickly with a 12-volt test light. Power here indicates that the problem is in the control switches, the wiring, the solenoid or the pump motor. Jump a wire temporarily from the battery cable to the energizing terminal of the solenoid to see if the pump starts to run. If it does, the problem is in the control switch or wiring; if the pump does not run, the problem is either the solenoid or the pump motor. If the solenoid makes a heavy clicking sound when energized, it's likely the motor; no sound would point to a bad solenoid.