Ford Grand Marquis Owner's Manual page 17

This light illuminates every time you turn the
ignition to the ON or START position (engine
off). The light should go off when the engine
starts and the alternator begins to charge.
If the light stays on or illuminates when the
engine is running, have the electrical system
checked as soon as possible.
Overdrive Off Indicator
The overdrive off indicator light
This light tells you that the Transmission Control
Switch (TCS) has been pushed. When the light is
on, the transmission will not shift into overdrive.
Depressing the button will return the vehicle to
"overdrive on" mode. The transmission 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.
NOTE: If the light does not come on when the
TCS is depressed or if the light flashes
when you are driving, have your
vehicle serviced at the first
opportunity. If this condition persists,
damage could occur to the
transmission.
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