Brake lights: Notes

WARNING: This page is about a different car, the 2001 Saab 9-3. However, it is still accessible from the selected car via links, so may be relevant.

The brake lights go on when the brake light switch is actuated.

Fig 1: Identifying Communication Flow - Brake Lights

Courtesy of SAAB-SCANIA OF AMERICA, INC.

Fig 2: Identifying Brake Lights Circuit Diagram

Courtesy of SAAB-SCANIA OF AMERICA, INC.

The brake light switch is powered with +30 via fuse 12. When the brake pedal is depressed, the brake light switch (29) closes and pin 48 on TWICE receives current.

The brake lights are powered from pins 1 and 25 via two resistors inside TWICE. The module measures the voltage drop across the two resistors and can in this way determine the current flowing through TWICE to the respective brake light circuits.

In the high-level brake light there are 16 LEDs (30RC) connected in parallel. These are powered and monitored from DICE pin 24. LEDs are used for this function because they light up very much quicker than a normal lamp bulb.

The high-level brake light on the Convertible has 5 lamp bulbs (30RC) and is monitored from DICE pin 24.

The brake light circuits are prepared for use with a trailer connector. In this case the circuits function in a similar way but they use fuse B (22a).