A first power unit (500, 550) for a vehicle or ground terminal comprising: a connector (502, 522) configured to connect the first power unit (500, 550) to a remote power unit (500, 550) over a power line having a plurality of wires; a power circuit (504, 552) configured to receive power from or provide power to the remote power unit (500, 550) over the power line; a controller (512, 556) configured to detect connection between the first power unit (500, 550) and the remote power unit (500, 550); one or more modems (530, 560) configured to transmit and receive data over the power line when the first power unit (500, 550) is connected to the remote power unit (500, 550), the one or more modems (530, 560) are configured to: automatically establish a data connection with one or more remote modems (530, 560) in the remote power unit (500, 550) over the power line in response to detection by the controller (512, 556) of the connection between the first power unit (500, 550) and the remote power unit (500, 550); and after establishing the data connection with one or more remote modems (530, 560), exchanging data with the one or more remote modems (530, 560) over the power line wherein the connector (502, 522) is configured to electrically connect a first subset of wires in the power line before electrically connecting a second subset of wires in the power line; and wherein the controller (512, 556) is configured to detect a signal on a wire in the second subset of wires and to initiate the data connection by the one or more modems (530, 560). a connector (502, 522) configured to connect the first power unit (500, 550) to a remote power unit (500, 550) over a power line having a plurality of wires; a power circuit (504, 552) configured to receive power from or provide power to the remote power unit (500, 550) over the power line; a controller (512, 556) configured to detect connection between the first power unit (500, 550) and the remote power unit (500, 550); one or more modems (530, 560) configured to transmit and receive data over the power line when the first power unit (500, 550) is connected to the remote power unit (500, 550), the one or more modems (530, 560) are configured to: automatically establish a data connection with one or more remote modems (530, 560) in the remote power unit (500, 550) over the power line in response to detection by the controller (512, 556) of the connection between the first power unit (500, 550) and the remote power unit (500, 550); and after establishing the data connection with one or more remote modems (530, 560), exchanging data with the one or more remote modems (530, 560) over the power line automatically establish a data connection with one or more remote modems (530, 560) in the remote power unit (500, 550) over the power line in response to detection by the controller (512, 556) of the connection between the first power unit (500, 550) and the remote power unit (500, 550); and after establishing the data connection with one or more remote modems (530, 560), exchanging data with the one or more remote modems (530, 560) over the power line wherein the connector (502, 522) is configured to electrically connect a first subset of wires in the power line before electrically connecting a second subset of wires in the power line; and wherein the controller (512, 556) is configured to detect a signal on a wire in the second subset of wires and to initiate the data connection by the one or more modems (530, 560).