Brake light filament monitor

Fig 1: Brake Light Filament Monitor Circuit Diagram

Courtesy of SAAB-SCANIA OF AMERICA, INC.

In TWICE, the current to each pin passes through a shunt resistor for that pin. In the event of filament failure, SID puts a fault message onto the bus. The control module generates an audible signal and puts the message REAR LIGHT FAILURE onto the display.