Pedal position sensor on the brake booster has nothing to do with shift lock or brakelights. It is only input info on pedal position for ABS. Shift lock is controlled by brake light switch and micro switch at shifter. When shifter is in park, micro switch on shifter is closed. When brake pedal is depressed, current flows from the switch through the closed micro switch and on to the solenoid. When out of park, open micro switch prevents solenoid activation evety time brakes are used. Common failures are micro switch, light switch at pedal, and electrical portion of ignition switch.