A lighting system for a vehicle includes a lamp and a deciding circuit to detect the number of abnormal light emitting elements or the abnormal elements in the lamp. The deciding circuit may be connected to a disconnection detecting circuit by one signal line to detect an abnormality of a particular one light emitting element, wherein the disconnection detecting circuit is adapted to provide to the signal line a potential corresponding to the particular light emitting element whose disconnection is detected and the deciding circuit is adapted to identify the abnormal light emitting element on the basis of the potential of the signal line.