Lincoln Navigator 4wheel drive 1998

See that this is an old problem. Some of the knobs could crack on the backside and allow the knob to rotate on the shaft without turning the shaft at all. If the knob is okay then go underneath the vehicle and disconnect the electric plug on the shift solenoid and Inspect for corrosion on the terminals. There is a problem which can happen if an indicator light burns out in the electric shift models. The length of the shift solenoid plunger is what determines whether you are in 2 wheel or 4 wheel drive, or high or low range. If the indicator light burns out, it changes the electric power and position of the shift solenoid plunger.