Abstract: An illumination system for illuminating the rear wheel assembly of a wheeled vehicle for a predetermined period of time in response to actuation of a turn signal. An auxiliary light and corresponding circuit are provided on the underside of a semi-trailer or other wheeled vehicle, the light being turned on in response to actuation of the turn signal on the same side of the vehicle so as to illuminate the rear wheel assembly. The light remains on for a predetermined period of time after the turn signal is turned off or deactuated, due to the dissipation of charge in a storage capacitor provided in the circuit. The circuit operatively associated with the auxiliary light is provided with a switching transistor as well as the storage capacitor, the transistor functioning to cause the auxiliary light to be illuminated when both (i) the vehicle's lights are on; and (ii) the turn signal on the appropriate side of the vehicle is actuated.