Luminous device, notably a lighting and/or signaling device, for a vehicle, comprising an optical device, a module and a light source positioned on said module assembled onto said optical device, the optical device and the module having first reference means comprising: - at least one slideway mounted on the optical device, said slideway having an interior reference face placed opposite an interior guide face, and - at least one extension extending from the module, said extension having a reference bearing face, opposite a contact face, said contact face comprising at least a first contact point and a second contact point, the contact face being arranged so that, when the extension has been introduced into the slideway in a direction of introduction, the contact face bears at the contact points (P1, P2) against the interior guide face, and that the slideway and/or the extension are elastically deformed locally at the contact point, the contact points (P1, P2) being positioned on several protuberances projecting from the contact face, the reference bearing face of the module being made to bear against the interior reference face of the slideway, characterized in that the first contact point is positioned before the second contact point on the contact face along the direction of introduction, in that the interior reference face and the interior guide face of the slideway form a given angle (a) between them about an axis which is parallel to the interior reference face and to the interior guide face of the slideway, and is substantially perpendicular to the direction of introduction of the extension into the slideway, the angle formed by the interior reference face and the interior guide face of the slideway being in the range from 1° to 10°, and preferably from 2° to 6°, in that the contact points lie within a plane of alignment forming an angle (a) with the reference bearing face about an axis (oy') which is parallel to the reference bearing face and to the plane of alignment and substantially perpendicular to the direction of introduction (o'x') of the extension into the slideway, in that said angle (a) which the plane of alignment and the reference bearing face make with each other is substantially equal to the angle formed by the interior reference face and the interior guide face of the slideway,and in that the module comprises two extensions, extending laterally on either side of said module, which are introduced into two slideways positioned on the optical device facing each other. - at least one slideway mounted on the optical device, said slideway having an interior reference face placed opposite an interior guide face, and - at least one extension extending from the module, said extension having a reference bearing face, opposite a contact face, said contact face comprising at least a first contact point and a second contact point, the contact face being arranged so that, when the extension has been introduced into the slideway in a direction of introduction, the contact face bears at the contact points (P1, P2) against the interior guide face, and that the slideway and/or the extension are elastically deformed locally at the contact point, the contact points (P1, P2) being positioned on several protuberances projecting from the contact face, the reference bearing face of the module being made to bear against the interior reference face of the slideway, characterized in that the first contact point is positioned before the second contact point on the contact face along the direction of introduction, in that the interior reference face and the interior guide face of the slideway form a given angle (a) between them about an axis which is parallel to the interior reference face and to the interior guide face of the slideway, and is substantially perpendicular to the direction of introduction of the extension into the slideway, the angle formed by the interior reference face and the interior guide face of the slideway being in the range from 1° to 10°, and preferably from 2° to 6°, in that the contact points lie within a plane of alignment forming an angle (a) with the reference bearing face about an axis (oy') which is parallel to the reference bearing face and to the plane of alignment and substantially perpendicular to the direction of introduction (o'x') of the extension into the slideway, in that said angle (a) which the plane of alignment and the reference bearing face make with each other is substantially equal to the angle formed by the interior reference face and the interior guide face of the slideway,and in that the module comprises two extensions, extending laterally on either side of said module, which are introduced into two slideways positioned on the optical device facing each other.