A motor vehicle ignition switch has a first and a second electrical circuit for detecting the angular position of a key in an ignition lock, with a rotor that is rotatable about a rotation axis so as to be able to selectively take an off position, a starting position, a running position, an on position and an intermediate position, distinct from each other; the second circuit is independent of the first circuit and defines a resistive divider; the first circuit has a first, a second and a third conductive laminas, electrically isolated from each other; the first circuit has two contacts, one of which is arranged on the third lamina in the running position and in the starting position and on the first lamina in the intermediate position.