Four Wheel Drive Indicator Lamp: Description and Operation
SHIFT INDICATOR (TRANSFER CASE)Part Time Indicator
A part time indicator is standard equipment on all instrument clusters. The part time indicator is located near the upper edge of the instrument cluster overlay, in the upper right quadrant of the cluster. The part time indicator consists of a stencil-like cutout of the words "PART TIME" in the opaque layer of the instrument cluster overlay. The dark outer layer of the overlay prevents the indicator from being clearly visible when it is not illuminated. An amber lens behind the cutout in the opaque layer of the overlay causes the "PART TIME" text to appear in amber through the translucent outer layer of the overlay when it is illuminated from behind by a Light Emitting Diode (LED) soldered onto the instrument cluster electronic circuit board. When the exterior lighting is turned ON, the illumination intensity of the part time indicator is one-step dimmable, which is adjusted using the panel lamps dimmer control ring on the left multi-function switch control stalk. The part time indicator is serviced as a unit with the instrument cluster.
The part time indicator gives an indication to the vehicle operator that a part time operating mode of the four-wheel drive transfer case is selected. On vehicles equipped with the standard Command-Trac four-wheel drive system, the part time indicator lights when the transfer case is engaged in the 4H or 4L positions. On vehicles in some markets where the Selec-Trac four-wheel drive system is an available option, the part time indicator lights when the transfer case is engaged in the 4 X 4 Part Time or 4 Lo positions. This indicator is controlled by a transistor on the instrument cluster electronic circuit board, and is controlled by a hard wired transfer case switch input to the cluster. The part time indicator Light Emitting Diode (LED) receives battery current on the instrument cluster electronic circuit board through the fused ignition switch output (Run-Start) circuit whenever the ignition switch is in the ON or Start positions; therefore, the LED will always be OFF when the ignition switch is in any position except ON or Start. The LED only illuminates when it is provided a path to ground by the instrument cluster transistor. The instrument cluster will turn on the part time indicator for the following reasons:
- Transfer Case Switch Input - Each time the cluster detects a ground on the 4WD switch sense (part time) circuit (transfer case switch closed = part time 4WD selected) the part time indicator will be illuminated. The indicator remains illuminated until the 4WD switch sense (part time) input to the cluster is an open circuit (transfer case switch open = part time 4WD not selected), or until the ignition switch is turned to the OFF position, whichever occurs first.
- Actuator Test - Each time the cluster is put through the actuator test, the part time indicator will be turned ON, then OFF again during the bulb check portion of the test to confirm the functionality of the LED and the cluster control circuitry.
The transfer case switch is connected in series between ground and the 4WD switch sense (part time) input to the instrument cluster. The transfer case switch input to the instrument cluster circuitry can be diagnosed using conventional diagnostic tools and methods. For further diagnosis of the part time indicator or the instrument cluster circuitry that controls the LED, (Refer to ELECTRICAL / INSTRUMENT CLUSTER - DIAGNOSIS AND TESTING).
Full Time Indicator
A full time indicator is standard equipment on all instrument clusters, but is only functional on vehicles in some markets where the Selec-Trac four-wheel drive system is an available option. The full time indicator is located near the upper edge of the instrument cluster overlay, in the upper right quadrant of the cluster. The full time indicator consists of a stencil-like cutout of the words "FULL TIME" in the opaque layer of the instrument cluster overlay. The dark outer layer of the overlay prevents the indicator from being clearly visible when it is not illuminated. A green lens behind the cutout in the opaque layer of the cluster overlay causes the "FULL TIME" text to appear in green through the translucent outer layer of the overlay when it is illuminated from behind by a Light Emitting Diode (LED) soldered onto the instrument cluster electronic circuit board. When the exterior lighting is turned On, the illumination intensity of the full time indicator is one-step dimmable, which is adjusted using the panel lamps dimmer control ring on the left multi-function switch control stalk. The full time indicator is serviced as a unit with the instrument cluster.
The full time indicator gives an indication to the vehicle operator that a full time operating mode of the four-wheel drive transfer case is selected. On vehicles in some markets where the Selec-Trac four- wheel drive system is an available option, the full time indicator lights when the transfer case is engaged in the 4 X 4 Full Time position. This indicator is controlled by a transistor on the instrument cluster electronic circuit board, and is controlled by a hard wired transfer case switch input to the cluster. The full time indicator Light Emitting Diode (LED) receives battery current on the instrument cluster electronic circuit board through the fused ignition switch output (run-start) circuit whenever the ignition switch is in the ON or Start positions; therefore, the LED will always be OFF when the ignition switch is in any position except ON or Start. The LED only illuminates when it is provided a path to ground by the instrument cluster transistor. The instrument cluster will turn on the full time indicator for the following reasons:
- Transfer Case Switch Input - Each time the cluster detects a ground on the 4WD switch sense (full time) circuit (transfer case switch closed = full time 4WD selected) the full time indicator will be illuminated. The indicator remains illuminated until the 4WD switch sense (full time) input to the cluster is an open circuit (transfer case switch open = full time 4WD not selected), or until the ignition switch is turned to the OFF position, whichever occurs first.
- Actuator Test - Each time the cluster is put through the actuator test, the full time indicator will be turned ON, then OFF again during the bulb check portion of the test to confirm the functionality of the LED and the cluster control circuitry.
The transfer case switch is connected in series between ground and the 4WD switch sense (full-time) input to the instrument cluster. The transfer case switch input to the instrument cluster circuitry can be diagnosed using conventional diagnostic tools and methods. For further diagnosis of the part time indicator or the instrument cluster circuitry that controls the LED, (Refer to ELECTRICAL / INSTRUMENT CLUSTER - DIAGNOSIS AND TESTING).