A/T Gear Position Indicator
How the Circuit WorksWhen the ignition is in ON (II) or START (III), battery voltage is supplied to the A/T gear position switch dimmer in the gauge assembly The dimming circuit supplies battery voltage to the indicator bulbs
When the combination light switch is in HEAD or PARK, battery voltage is supplied through the taillight relay to the dimming circuit, which then dims the indicator light through the RED wire to the level requested When the transmission is in Park, Reverse Neutral, D, 3/M, 2, or 1 the A/T gear position switch grounds the appropriate bulb, and the bulb comes on When the transmission is in Drive, the transmission control module (TCM) controls the indicator by sending a signal through the YEL/BLK wire to turn on the transistor The transistor connects the D indicator to ground, and the bulb comes on
The D indicator is used to display transmission control module (TCM) trouble codes so it comes on momentarily as a bulb check whenever you turn the key on When commanded to display codes, the TCM sends a signal through the YEL/BLK wire to turn on the transistor The transistor grounds the dimming cancel input of the dimming circuit, and the TCM then displays trouble codes by turning the D indicator on and off at full brightness