Lighting unit and method for mounting a lighting unit

A first fastening point (5) holds the casing immovably with respect to the bodywork. It comprises closely-interlocking holding components (9, 9'), one (9') of which is fixed in position, on the bodywork section (4). Once located, the casing can only be moved in a direction opposite to that of attachment. An Independent claim is included for the corresponding method of fastening.