Land Rover Discovery Owners & Service Manuals

Land Rover Discovery: Central Junction Box

The CJB controls the exterior lighting system through interconnections as follow:

  • Left steering column multifunction switch
  • Side lamp position
  • Low beam position
  • Automatic ('AUTO') position (if fitted)
  • Front fog lamp switch (if fitted)
  • Rear fog lamp switch
  • Turn signal indicators
  • High beam switch
  • Headlamp flash
  • Stop lamp switch
  • Manual headlamp LEVELLING control switch (halogen only)
  • Hazard warning lamp switch
  • Rain/light sensor (LIN signal).


Two 60 Amp fusible links in the BJB protect the power feed to the CJB, left and right lighting circuits respectively. All exterior lighting circuits are protected by Field Effect Transistors (FETs), located in the CJB, which can detect overloads and short circuits.

The FETs respond to heat generated by increased current flow caused by a short circuit. On a normal circuit this would cause the fuse to blow. The FETs respond to the heat increase and disconnect the supply to the affected circuit. When the fault is rectified or the FET has cooled, the FET will reset and operate the circuit normally. If the fault persists the FET will cycle, disconnecting and reconnecting the power supply. The CJB stores fault codes which can be retrieved using a Land Rover approved diagnostic system. The fault code will identify that there is a fault on a particular output which assist in fault detection.


The exterior lighting system is used for arm and disarm requests. When the driver locks or unlocks the vehicle, a visual indication of a successful lock or unlock request is displayed to the driver by the hazard flashers.

For additional information, refer to: Anti-Theft - Active (419-01A Anti-Theft - Active, Description and Operation).


When the ignition is in the off (power mode 0) or auxiliary (power mode 4) mode and the left steering column multifunction switch is in the side lamp or Low beam position, a warning chime will sound if the driver door is opened. This indicates to the driver that the exterior lights have been left on. The chime is generated from Instrument Cluster (IC) sounder on receipt of a lights-on signal, a door open signal and an ignition off signal from the CJB on the HS CAN bus.


In the event of an accident of a severity to activate and deploy the airbags, the Restraints Control Module (RCM) sends a request to the CJB via the HS CAN bus to activate the hazard warning lamps. The hazard warning lamps will continue to operate until the ignition mode is changed to the auxiliary power mode 4, or the off power mode 0, or the RCM no longer transmits the crash signal.


The CJB controls a headlamp delay function which illuminates the driveway after leaving the vehicle. The CJB activates the low beam headlamps for the required delay period. The delay timer is set within the IC 'Vehicle Set-up Menu'. The default timing is 30s, but the timing can be changed to between 0s (OFF), 30s (default), 60s, 120s and 240s.

For additional information, refer to: Information and Message Center (413- 08 Information and Message Center, Description and Operation).



NOTE: A = Hardwired; AN = High Speed (HS) Controller Area Network (CAN) Powertrain bus; O = Local Interconnect Network (LIN) bus.


  1. Central Junction Box (CJB)
  2. Headlamp LEVELLING Control Module (HLCM)
  3. Headlamp assemblies
  4. Reverse lamp switch
  5. Rain/light sensor
  6. Front fog lamps
  7. Side repeater lamps in door mirrors
  8. License plate lamp
  9. Rear fog lamps
  10. Tail lamp assemblies
  11. HMSL
  12. Ground
  13. Fuse
  14. Left steering column multifunction switch
  15. Clockspring
  16. Stop lamp switch
  17. Hazard warning lamp switch
  18. Battery
  19. Battery Junction Box (BJB)
  20. Height sensors

Exterior Lighting Specifications

Torque Specifications

Torque Specifications


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