Circuit description

During 2 wheel drive operation, 4WD switch is open (OFF), switched ignition voltage is applied through 4WD indicator lamp and sent to ECM (PCM) and monitored by EBCM.

When the operator selects 4 wheel drive, 4 wheel drive switch is closed (ON), ECM (PCM) respond by grounding 4 wheel drive circuit which will illuminate 4WD indicator lamp. EBCM will sense that voltage is pulled low on the 4WD lamp circuit, indicating vehicle is in 4WD.