Light Switch

The light switch is located to the left of the steering column. It is a single component and includes the following controls:

• Rotary knob light switch (including Automatic position).
• Fog light push button.
• Dimmer potentiometer thumb wheel.
• Button for EMF (parking brake).
• Button for opening trunk (TOEHKI).
  Fig 1: Identifying Light Switch

  Courtesy of BMW OF NORTH AMERICA, INC.

he switches for trunk opening and EMF are interpreted separately by their respective control units.

The light switch uses a 5 volt reference supplied by the LM and provides the position of the rotary knob light switch over two wires.

When the switch is open, the LM reads 5V. When the switch is closed, the LM reads 2.5V. A value of over 6.75 volts represents a fault and activates the emergency operation of the LM.

Fig 2: Identifying Light Switch Schematic

Courtesy of BMW OF NORTH AMERICA, INC.

Interpretation of the 4 light switch positions is based on the switch logic over the two wires.

1 = switch closed

0 = switch open

The foglight switch is similarly interpreted as a high low signal over its own wire.