Abstract: A simple and inexpensive, mechanically coupled automatic guidance system for tractors comprising a ground line sensor which is directly coupled to a steering system comprising limited, partial, spatial disengagement or play about a narrow steering angle within which the automatic guidance system provides steering control, unencumbered by the forces of the primary steering system, especially the steering forces of a power-steered-tractor. The play in the steering system provides spatial relief of steering forces which could not otherwise be overridden by a purely mechanical system. The ground line sensor comprises three degrees of freedom permitting adjustable variation to the shape, breadth, and attitude of the sensor to conformably match a previously prepared ground line. At least two movement degrees of freedom allow the sensor to horizontally and vertically follow ground line and tractor path anomalies while providing feedback to the automatic guidance system.