Ford 1999 Windstar Owner's Manual page 157

Always set the parking brake fully and make sure the gearshift is
securely latched in P (Park).
Never leave your vehicle unattended while it is running.
R (Reverse)
With the gearshift in R (Reverse),
the vehicle will move backward. You
should always come to a complete
stop before shifting into and out of
R (Reverse).
N (Neutral)
With the gearshift in the N
(Neutral) position, the vehicle can
be started and is free to roll. Hold
the brake pedal down while in this
position.
Overdrive — column mounted gearshift with O/D off switch
The Overdrive position with the
O/D OFF switch not depressed is
the normal driving position for this
automatic overdrive transaxle. When
your vehicle cruises at a constant
speed for any length of time, this fourth gear will increase your fuel
economy.
Overdrive may not be appropriate
for certain terrains. If the transaxle
shifts back and forth between third
and fourth gears while you are
driving hilly roads or if your vehicle
requires additional power for climbing hills, press the O/D OFF switch.
The transaxle will be in the "overdrive on" mode when the vehicle is
started even if the O/D OFF mode was selected when the vehicle was
last shut off.
Driving
O/D
ON/OFF
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