WARNING: This page is about a different car, the 2016 RAM 3500 HD and 2016 RAM 2500 HD. However, it is still accessible from the selected car via links, so may be relevant.
Fig 1: Gearshift Lever Assembly Components
Courtesy of CHRYSLER GROUP, LLC
The Brake Transmission Shifter Interlock (BTSI), is a solenoid operated system. It consists of a solenoid permanently mounted on the gearshift lever assembly.