Transmission Control (TC) Switch
WARNING: This page is about a different car, the 2009 Ford Mustang. However, it is still accessible from the selected car via links, so may be relevant.
The transmission control (TC) switch is a momentary contact switch that is located on the floor mounted selector lever. Pushing the TC switch will either disengage or engage the overdrive function of the automatic transmission. If OVERDRIVE is disengaged, the word O/D OFF will illuminate on the instrument cluster.