Abstract: An automatic guidance system for towed vehicles is disclosed comprising a marker, a position sensor, an electronic operational amplifier circuit, an electrical servo controlled hydraulic valve, and a hydraulically controlled swinging draw bar hitch. The position sensor comprises a follower to follow the furrow mark in the ground made by the marker on the preceding pass of the farm implement over the ground and variable resistors mounted on the followers electrically connected to the amplifier circuit. The electrical servo controlled hydraulic valve is driven by the operational amplifier circuit in response to the varying output voltages received from the variable resistors responding to the position of the follower. The position of the towed implement relative to the furrow mark is adjusted by the action of the hydraulically controlled swinging draw bar responding to the operation of the electrical servo controlled hydraulic valve.