If the car cannot be raised on a lift or jack stands to confirm the presence of the overdrive unit at the tail end of the gearbox, check for an overdrive switch at the following locations:
- On the dash (which is usually surrounded by a telltale plinth)
- On the gearshift knob
- For most Triumph models, the overdrive is engaged by a stalk on the steering column that is located adjacent to the stalk for the turn signal indicators