The ornamental design for the light assembly for an automobile, as shown and described.
FIG. 1 is a front view of the light assembly for an automobile, showing my new design integrated into a left-side of an automobile; the automobile does not form a part of the claimed design and it is shown for illustrative purposes only;
FIG. 2 is a top, perspective view thereof;
FIG. 3 is a top, perspective view of the light assembly for an automobile integrated into rear of an automobile; the automobile does not form a part of the claimed design and it is shown for illustrative purposes only; the left-side part of the light assembly for an automobile and the right-side part of the light assembly for an automobile are mirror symmetrical;
FIG. 4 is a front view of the left-side part thereof;