A road finisher has a terminal box from which an electric supply circuit originates to supply electric current to at least one electric heating element for heating work components. A device for supervising the function of the at least one electric heating element includes an induction coil at the terminal box to sense current in the supply circuit and an indicator circuit, preferably of a light emitting diode, is connected to the induction coil for detecting and indicating a voltage induced in the induction coil by the current flowing in the supply circuit of a heating element. In a preferred embodiment, a cable gland is attached to the control box through which a current supply wire of the electric supply circuit passes, and an induction coil is located in the cable gland to sense the current in the supply wire.