Abstract: A vehicle turn signal malfunction warning system that alerts the vehicle driver when a turn signal indication is not cancelled after a predetermined time period comprises a modular housing that is plug-compatible with all standardized flasher units in use, requires no wiring to be connected to the turn signal system or to the vehicle electrical system. The system includes a full-wave rectifier connected across the inputs of the standard turn signal flasher, and is powered solely by the voltage derived from the turn signal system. The warning system includes a first time base circuit, a second time base circuit, a gating means, and a tone generator means. The first time base circuit is arranged to be fully charged by the first turn signal pulse through the full-wave rectifier, and to discharge approximately 2.5 seconds after the turn signal pulse train ends. The second time base circuit begins charging when the first time base is fully charged, and accumulates a charge until the first time base circuit resets.