Truck tractors in a transportation fleet include a transponder that transmits a unique tractor identifier to a connected trailer using a Power Line Communication (PLC) bus device. The information transmitted typically includes a manufacturing unique ID for the tractor and an optional user defined ID. The user defined ID may include a fleet division code. The tractor ID and/or fleet ID codes determine how the trailer is hooked up. In particular, with detection of a connected state signal from the PLC bus, together with receipt of tractor identification code(s) from the tractor, the trailer tracking device can now communicate the coupling event information to a centralized location, such as via a cellular telephone connection.