Do you know anything about automotive electronic's ? The brake pedal position sensor is a input to the BCM - body control module ,the BCM turns on the stop lamps . Possible short in the (CHMSL ) - center high mount stop lamps , wiring etc.... Causing problem inside the BCM . Do you know what wiring diagrams are ? Free one's here http://www.bbbind.com/free-tsb
Enter vehicle info. year , make , model an engine size . Under system click on lighting , then under subsystem click on exterior lighting . Click the search button then the blue link's . First diagram show's the brake pedal position sensor input to the BCM ,lower right . Second diagram show's BCM power supply to the third brake light (CHMSL) . Having a qualified repair shop with a professional scan tool to check for DTC'S - diagnostic trouble code's could save a bunch of time in diagnosing the problem .
The body control module (BCM) supplies voltage to the center high mount stop lamp (CHMSL) and the powertrain control module (PCM) when the stop lamps are active.
DTC B3903 Stop Lamp Relay Circuit
The body control module (BCM) is responsible for controlling the stop lamps. When the driver presses the brake pedal, the BCM will receive a signal from the brake pedal position sensor. The BCM then supplies battery positive voltage to both left and right stop lamp assemblies and to the center high mounted stop lamp (CHMSL). The stop lamps are grounded at G401 and G403. The CHMSL is grounded at G302.