Ford 1996 Thunderbird Manual page 171

Transmission Control Indicator Light (O/D OFF)
is located on the instrument panel. You can put
the gearshift lever in any of the several
positions.
The OVERDRIVE OFF light is off (not
illuminated) during normal vehicle operation.
This allows the transmission to upshift and
downshift from 1st through 4th gears. When the
TCS is pressed, the Transmission Control
Indicator Light will illuminate (O/D OFF) on the
instrument panel. When this O/D OFF is
illuminated the transmission will upshift and
downshift from 1st through 3rd gears.
If the O/D OFF 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.
To return the transmission to normal operation
(1st through 4th gear) depress the TCS again.
This switch may be used to cancel overdrive any
time the vehicle is being driven. Each time your
vehicle is started, the overdrive system will
automatically be in the normal overdrive mode
and the light will not be illuminated.
When to use D (Overdrive)
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.
168