What is this?

Your picture is the EGR delay typically mounted on the passenger side firewall above the blower motor. The seatbelt interlock sits on the driver side near the wiper fluid bottle and mounts with an L-shaped bracket. The seatbelt interlock has a round cylindrical area that you can use a pointed object like a pencil point to override the seatbelt not being buckled to get the starter to crank.