Transmission Control Switch (TCS)
WARNING: This page is about a different car, the 2003 Lincoln Aviator. However, it is still accessible from the selected car via links, so may be relevant.
The transmission control switch (TCS) is a momentary contact switch that is located on the console-mounted transmission range selector lever. Pushing the TCS will either disengage or engage the overdrive function of the automatic transmission. If the OVERDRIVE is disengaged, the word O/D OFF will illuminate on the instrument cluster.