Possible causes, elimination, notes

Check with the System Tester 2 via the "Input signals" menu. Press the brake pedal after selection of the stop-light switch.

Required display: Display in screen changes from "not actuated" to "actuated".

• Pull off wires on the stop-light switch (No. 1). Test the stop-light switch with a multimeter (remove switch for the test if necessary).
  Fig 1: Locating Stop Light Switch

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• Check stop-light switch adjustment (operating point) (see ADJUSTING BRAKE PUSH ROD (ADJUSTING STOP LIGHT SWITCH) ).
• Check wiring according to the wiring diagram.