electrical train line 12 fig3 which is part of a locomotive 39 s electrical control circuits as known to the art as indicated by the labeling in fig3 included within the train line 12 is an electrical conductor designated as the reverse line for carrying an electrical signal indicating when the locomotive reverses direction thereby signifying travel in a forward direction and a reverse direction the train line also includes power lines by which connections are made to a nominal 72 volt dc power supply in the construction described in u s pat no 4 561 057 these two portions of the train line are external means for providing inputs directly to the on board unit 2 however in the present invention these lines are also connected to the on board unit 10 other inputs including the remaining signals of the train line 12 and those of pressure transducers 14 are effectively connectible to the on board unit 2 to the extent that the information from such signals is conveyed through the new on board unit 10 to which the train line 12 and the transducers 14 are connected it is contemplated that other signals e g fuel flow rate signals bell and horn pressure switch signals can be connected.