RAM 3500 Truck 4WD L6-5.9L DSL Turbo VIN C (2002)
Four Wheel Drive Indicator Lamp: Description and Operation
SHIFT INDICATOR (TRANSFER CASE)
A four-wheel drive indicator is standard equipment on all instrument clusters. However, on vehicles not equipped with the optional four-wheel drive
system, this indicator is mechanically disabled. The four-wheel drive indicator is located near the lower edge of the instrument cluster overlay, to the
right of center. The four-wheel drive indicator consists of a stencilled cutout of the text "4WD" 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 "4WD" text to appear in amber through the translucent outer layer of the overlay when the indicator is illuminated from
behind by a Light Emitting Diode (LED) soldered onto the instrument cluster electronic circuit board. The four-wheel drive indicator is serviced as a
unit with the instrument cluster.
The four-wheel drive indicator lamp gives an indication to the vehicle operator that a four-wheel drive operating mode is engaged. The indicator will be
illuminated when either high range (4H) or low range (4L) have been selected with the transfer case shift lever. This indicator is controlled by a
transistor on the instrument cluster circuit board based upon the cluster programming, and a hard wired input from the four-wheel drive switch on the
front axle disconnect housing. The four-wheel drive indicator Light Emitting Diode (LED) receives battery current on the instrument cluster electronic
circuit board through the fused ignition switch output (st-run) circuit whenever the ignition switch is in the ON or Start positions; therefore, the lamp will
always be OFF when the ignition switch is in any position except ON or Start. The LED only illuminates when it is switched to ground by the instrument
cluster transistor.
The four-wheel drive switch is connected in series between ground and the four-wheel drive switch sense input to the instrument cluster. The four-wheel
drive switch input to the instrument cluster circuitry can be diagnosed using conventional diagnostic tools and methods.
