Brake On-Off (BOO) Switch
WARNING: This page is about a different car, the 1995 Ford Pickup, 1995 Ford F-Super Duty, and 1995 Ford Cab & Chassis. However, it is still accessible from the selected car via links, so may be relevant.
BOO switch is wired to brakelight circuit. It signals the PCM when the brake is applied. The BOO input is used primarily by the torque converter clutch lock/unlock strategy.