Lincoln 1997 Town Car Owner's Manual page 179

Overdrive is the usual driving position for an
automatic overdrive transmission. It works the same
way Drive works, automatically upshifting or
downshifting as the vehicle speeds or slows.
However, Overdrive also shifts into a fourth gear —
an overdrive gear — when your vehicle cruises at
an appropriate consistent speed for any length of
time. This fourth gear will increase your fuel
economy when you travel at cruising speeds.
When to use Drive (j — with
Transmission Control Switch activated)
Overdrive may not be appropriate for certain
terrain. If the transmission shifts back and forth
between Third and Fourth gears while you are
driving on hilly roads or if your vehicle does not
have adequate power for climbing hills, depress the
TCS.
You can depress the TCS at any speed.
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When to use 2 (Second)
Use 2 (Second) for start-up on slippery roads or to
give you more engine braking to slow your vehicle
on downgrades.
When to use 1 (Low)
Use 1 (Low) when driving down steep grades. It
gives more engine braking to slow your vehicle than
2 (Second) on the downgrades. You can upshift
from 1 (Low) to 2 (Second) or from 1 (Low) to
Overdrive at any speed.
P (Park)
Always come to a complete stop before you shift
into P (Park). Make sure that the gearshift is
securely latched in P (Park). This locks the
transmission and prevents the rear wheels from
rotating.