Where is the button to turn off overdrive on a 1999 Ford Taurus?

The 1999 Ford Taurus doesn't have an overdrive off button. Overdrive is controlled by the transmission's shift lever. To turn off overdrive, you'll need to manually shift the transmission into a lower gear (usually by moving the shifter to the left and down from the "D" position). The exact position and labeling will vary slightly depending on the specific transmission type in your Taurus, but it's typically a "1" or "2" position on the shifter.