Ford Windstar Owner's Manual page 21

Instrumentation
The low windshield washer indicator light
Low Fuel Indicator Light
This light comes on when your fuel gauge indicates
approximately 1/16 of a tank. The ignition must be turned to
ON in order for this light to come on.
The low fuel indicator light
Gauges
Fuel Gauge
The fuel gauge displays approximately how much fuel is in the
fuel tank only when the ignition is ON. For proper fuel gauge
indication after adding fuel, the ignition should be in the OFF
position while the vehicle is being refueled.
The fuel gauge indicator may also vary slightly when the
vehicle is in motion. With the ignition OFF, the fuel gauge
indicator may drift from the ignition ON position as well.
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