A harvester is described having a metal detection system (58) capable of resolving the position of a metal foreign object across the width of the feeder section (20, 21, 26, 27) of the harvester. Means mounted externally of the harvester are provided for emitting at least one of an audible and a visible pulsed signal of which the pulse sequence is encoded to indicate the position of a detected foreign object in the feeder section (20, 21, 26, 27).