Discovery II
ALARM SYSTEM AND HORN
86-4-6
DESCRIPTION AND OPERATION
Door latch switches
The BCU uses the door latch switches to indicate if a door is open or closed. There is a door latch switch within every
door latch assembly, including the tail door latch assembly.
Input/Output
The input from the door latch switches to the BCU is either zero volts or an open circuit. Zero volts indicates the door
is open. An open circuit indicates that the door is closed. When the BCU sees an open circuit, it pulls the input high
internally.
The driver's door latch switch has a dedicated signal input to the BCU. This allows the BCU to identify the driver's
door position.
The BCU use a common signal input for the remaining door latch switches.
TestBook provides the ability to monitor the real time state of the door latch switches. Remember that the driver's
door is always in a known state. The remaining doors are combined into a single state. The BCU cannot distinguish
the state of the individual doors, other than the driver's door.