Four Wheel Drive Indicator Lamp: Description and Operation

SYSTEM OPERATION
On vehicles equipped with the optional four-wheel drive system, a four-wheel drive indicator lamp is located in the instrument cluster. This lamp lights any time the front axle is engaged in a four-wheel drive operating mode.

When the ignition switch is in the On position, battery voltage is supplied to one side of the indicator lamp bulb. A normally-open, plunger-type, four-wheel drive switch threaded into the front axle disconnect housing is hard-wired in series between the other side of the indicator lamp bulb and ground.

When the transfer case is shifted into the 4L or 4R positions, a vacuum switch on the transfer case directs engine vacuum to a vacuum motor on the front axle disconnect housing. The vacuum motor actuates a shift fork within the front axle, which engages or disengages the inner and outer halves of the front axle shaft. The shift fork movement also actuates the plunger of the four-wheel drive switch, opening or closing the ground path for the indicator lamp.