A system is provided for the control of two transmissions in a multi-combination vehicle having at least two engines, each engine operatively coupled to one transmission. Each transmission has its own electrical power source and an electronic control unit. The system includes an electronic gear selector having a power input and a variable output representative of a desired operation of each of the transmissions. The system further includes a gear selector control module that is provided power from each of the electronic control units and selectively provides power to the power input of the electronic gear selector from a selected one of the electronic control units. The variable output of the electronic gear selector is in communication with at least the selected one of the electronic control units. The electronic gear selector further includes a display for displaying diagnostic codes from an electronic control unit, the selector selectively displaying diagnostic codes form the electronic control unit that it is provide power from. In other embodiments, the system of the present invention is effective for the control of multi-combination vehicles having at least three engines.