Abstract: The slider, to which the rear wheels of an automotive trailer are secured, can be released from that trailer to permit limited forward or rearward movement of that trailer relative to that slider. Sensors are spaced short distances apart along a portion of the length of the trailer, and openings in longitudinal members of that trailer are precisely oriented relative to those sensors. Power-operated locking pins can be selectively withdrawn from those openings to permit relative movement between that slider and that trailer, and thereafter those pins can be driven into those openings to prevent such relative movement. A readout is mounted in the cab of the tractor to enable the driver to precisely determine the relative positions of the slider and trailer and to effect power-controlled unlocking and locking of that trailer and slider.