How to Troubleshoot Forklift Electrical Circuits: A Complete Guide

Common electrical circuit faults mainly include short circuits, open circuits, grounding (short-to-ground), poor contact at connections, and failure of control devices.

Visual Inspection of Electrical Circuit Conditions

When a driver identifies a fault, a visual inspection of the vehicle’s entire electrical circuit should be performed. The main items to check include:

01  Fastening Condition

All electrical components and wiring should be securely fixed. The outer housings must be intact, and all parts should be complete and undamaged.

02 Contact and Cleanliness

Check whether all connectors are fully inserted and whether grounding points are tight. Inspect all contact points for signs of corrosion, oil contamination, or burning.

03 Insulation and Shielding Condition

The insulation layer of wires should be free from damage and aging. Any exposed wiring must be wrapped with electrical tape. The shielding of the wires should show no signs of breakage or abrasion.

04 Fuse and Relay Condition

All fuses and relays should be firmly installed, with wires connected securely and making good contact. The selected fuses and relays must be complete and meet the circuit’s rated requirements.

05 Switch Operation Condition

All switches and buttons should operate smoothly without sticking or malfunction.

Instrument Testing

Using instruments or dedicated testers to inspect electrical circuits allows for accurate identification of fault locations, thereby facilitating troubleshooting.  

When electronic components are used in circuits, the "spark test" method is not permitted for circuit inspection. Instead, a voltmeter or DC test light should be used.

Voltage Testing

Measuring voltage at relevant points can help assess the technical condition of the starting and power systems. As part of the regular maintenance for internal combustion forklifts, it plays a significant role in ensuring the proper use of the electrical system and the timely resolution of faults.

01 Measuring Battery Voltage

Turn on the headlights for approximately 30 seconds to eliminate the battery’s "surface charge." Then, turn off the headlights and measure the voltage between the positive and negative terminals. The voltage should be above 12.2V (for 12V electrical systems) or 24.5V (for 24V electrical systems).

02 Measuring Starting Voltage to Assess Battery, Starter, and Connections

Remove the high-voltage wire from the ignition coil (for gasoline engines). Turn the ignition switch to the start position and crank the engine. Within 15 seconds, the voltage across the battery terminals should be at least 9.6V (or 19.5V for 24V systems). If the voltage is lower, potential issues may include:  

- Corroded or poorly connected battery terminals;  

- Over-discharged or faulty battery;  

- Faulty starter.

03 Measuring Voltage to Assess Generator and Voltage Regulator Condition

Start the engine and run it at approximately 2000 rpm. Measure the voltage at the generator or battery terminals. The voltage should be between 13.5–14.8V (for 12V systems) or 27.5–29.5V (for 24V systems). Alternatively, observe the onboard voltmeter: if the voltage reading increases by at least 2V compared to pre-start levels, it is normal. If the reading exceeds 15V (or 30V for 24V systems), the voltage regulator may be faulty. For accurate results, turn on the headlights or auxiliary electrical devices. If the reading is below 13.5V (or 27V), potential causes include:  

- Loose drive belt;  

- Corroded or poorly connected wiring;  

- Faulty voltage regulator;  

- Faulty generator.

Measuring Voltage Drop in Circuits

The voltage drop test method can be used to inspect wires, battery cables, and connections. Although an ohmmeter can measure circuit resistance, the low voltage and small current often fail to reflect actual conditions. Therefore, it is more reasonable to assess wire and connection conditions by measuring the voltage drop under normal operating current.  

Use a voltmeter with a range of 0–3V and an accuracy of 1.0 class or higher. Activate the circuit to its operational state. The typical voltage drop for general circuits is 0.1V, while for starting circuits, it should not exceed 1V.

Battery Leakage Test

A battery leakage test can identify faults such as grounding issues or insulation damage. Turn off all electrical equipment switches and measure the current between the battery negative terminal and the ground. The current should generally not exceed 30mA (or 300mA for forklifts equipped with electronic control systems). If the reading exceeds these values, it indicates battery leakage. Potential causes include:  

- Leakage or poor insulation in circuit switches or wiring;  

- Short-circuited generator diodes or excessive leakage current;  

- Faulty voltage regulator or electronic control unit;  

- Doors, storage compartments, or luggage compartments not fully closed or faulty switches.  

Open Circuit and Short Circuit Inspection

01 Open Circuit Inspection

Use a test light or dedicated tool to check for open circuits. Connect the test light or tool between a circuit connector and a ground point. Turn on the relevant switch. If the light does not illuminate, an open circuit is present.  

02 Short Circuit Inspection 

A short circuit in the circuit will cause the fuse to blow. Before replacing the fuse, identify the root cause. Common methods include:  

a.Using an Ohmmeter: Connect one probe to a ground point and the other to the fuse terminal. A resistance value of zero or very low indicates a short circuit. Disconnect the electrical devices controlled by the fuse one by one. When the resistance increases, the disconnected device has a short circuit fault.  

b. Using a Buzzer: Connect a buzzer across the fuse terminals. If the buzzer sounds, a short circuit exists. Disconnect the controlled electrical devices one by one. When the buzzer stops sounding, the disconnected device has a short circuit.  

c. Using a Circuit Interrupter and Gauss Meter: Connect the circuit interrupter to the fuse terminals. Use the Gauss meter to detect the pulsed magnetic field around the wiring along the circuit. The point where the needle stops moving indicates the short circuit location.  

Mastering troubleshooting—from visual checks to voltage tests—is essential for your forklift's electrical health. Always prioritize safety. For complex problems or if you're unsure, consult the manual or a certified technician. A well-maintained electrical system ensures a reliable, efficient forklift.If you need forklift parts, please contact us!