Differential Lock Indicator: Testing and Inspection

Differential Lock Indicator Inoperative

Circuit Description

The differential lock indicator lamp is located in the instrument cluster. Voltage is supplied from the IGN SW circuit breaker to the differential lock indicator through the ignition 3 voltage circuit. When the ignition switch is in the START position, current will travel through the bulb test signal circuit to the ignition switch grounding internally causing the differential lock indicator to illuminate. This lets the driver know that the indicator is functioning properly.

When the differential lock control valve is placed in the ON position this allows air pressure to build up in the system. The air pressure closes the differential lock switch providing ground for the differential lock switch signal circuit. This completes the indicator circuit illuminating the differential lock indicator.

Test Description

The numbers below refer to the step numbers on the diagnostic table.
2. This step tests for an intermittent condition.
3. This step checks for a short to voltage.
4. This steps isolates the bulb test signal circuit and the differential lock signal circuit.
5. This step tests the differential lock switch signal for proper voltage.
6. This step tests the differential lock ground circuit for continuity.
7. This step tests the ignition 1 voltage circuit for proper voltage.