Instrument lighting

The instrument lighting lights up the instrument cluster and the operating switch.

Brief description of components

Light switch

The light switch consists of

• Rotary switch for sidelights and low beam (and special equipment Automatic Light Control)
  
• Two buttons for fog lights and rear fog light
  
• Potentiometer for dimmer of panel illumination
  
• Potentiometer for manual headlight vertical aim control in the case of halogen headlights
  

Power supply: The switch is supplied with 5 Volts by the light module.

If the power supply is defective, the light remains ON: the light is automatically switched on if

• the cables to and from the light switch have been cut or
  
• are switched to earth
  
• are at 12 V.
  
• For safety reasons, the light switch can only be switched OFF if there is 5 V at both switch outputs to the light module. If a short circuit means that there is once 5 V and once 12 V, the light can not be switched OFF: low beam and Automatic Light Control remain ON.
  

Light module

The light module controls and monitors the vehicle lights. Information is received and sent via the data bus K-CAN SYSTEM.

In the case of the special equipment xenon headlights, the defects of the xenon headlights are evaluated in the light module.

Emergency operation properties of the light module: The light module is supplied with terminal 30 twice.

If a terminal 30 fails, the following are activated:

• Front lighting: low beam and parking light (each on one side).
  
• Rear lighting: On one side, the outer sidelights/brake lights are activated. On the other side, the inner taillights are activated. The vehicle thus still has lights on both sides. Confusion with a one-track vehicle (motorcycle) is excluded.
  
• Brake light: One side of the brake lights is activated with normal power (ECE coding). This leads to ”one-track” braking, as if for example one brake light had failed.
  

In the case of a failure of the processor, emergency operating mode is activated. Emergency operating mode involves hardware that is completely independent of the light module. Emergency operation properties with failure of the processor:

• Vehicle lighting: At terminal 15 On, the following are switched on: Front low beam and outer rear sidelights / brake lights left and right. The outer sidelights / brake lights left and right are not, as would be normal, dimmed to 10% of their brightness, but operated with full power. This ensures the function of the vehicle lighting irrespective of the position of the light switch.
  
• Brake light: With terminal 15 On, the left and right brake lights are switched on when the brake-light switch is operated (via a hard-wired, direct line from the brake-light switch to the lamp drivers).
  

Function defects with failure of the processor:

• No turn indicators and hazard warning lights, no high beam, no headlight flasher, no fog lights, no rear fog light, no third brake light
  
• No communication across the K-CAN SYSTEM.
  
• No communication with the trailer module
  

Main functions

Brightness control of the instrument lighting

The light module supplies the voltage for the instrument lighting.

Dependent on the following factors:

• the potentiometer setting in the light switch
  
• the basic brightness measured in the instrument cluster.
  

The data exchange from the instrument cluster to the light module is via the K-CAN

The output on the light module for terminal 58g is shortcircuit-proof.

The output voltage is pulse-width modulated.