Abstract: A rotary prime mover, preferably an electric motor, is remotely operable from the cab of the vehicle. A linkage couples the rotary prime mover to the pins of the slider assembly, wherein rotation of the rotary prime mover selectively moves the pin in and out registry with holes in a pair of rails on the trailer to prevent and permit relative movement between the rear tandem axle assembly and the trailer. A pin sensor is coupled to the linkage to detect whether the pins are in or out of registry with the holes in the rails and a counter is coupled between the rear tandem axle assembly and the trailer to determine with which of the holes in the rails the pins are aligned. A visual display is provided in the cab and coupled to the pin sensor and counter to communicate to the operator the registry of the pins and with which of the holes the pins are aligned.