How an Accord's Brake
lamp failure sensor
When S6 is
depressed and Q3 detects positive (high) on the
input then the lamp indictor lights up indicating
an open in one or more the failure sensors. When
negative (zero volts) meets up at the bottom of
R6, the input to Q3 becomes zero volts, and
therefore, Q3 does not pass current to the lamp
and the indicator lamp does not light.
terms, if the one of the bulbs doesn't light up
then the indicator lamp will light up. This
happens right after the driver steps on the
brake. This car uses a magnetic reed type.