Embodiments of the present disclosure provide a sealing device suitable for a connection between an electrical conductor insulated with PVC or silicone, leaving one end of the conductor exposed, and a contact element electrically connected to the conductor. The contact element, which can be a flat conductor, is enclosed in a jacket made of a semi-crystalline thermoplastic material. The contact element is exposed in the area of bonding with the conductor. According to the present disclosure, a sleeve-shaped adapter of a semi-crystalline thermoplastic material is inserted, surrounding the conductor with a gasket in an end area of the PVC or silicone insulation. Since the adapter is in the shape of a sleeve it can be pushed integrally over the electrical conductor. If the conductor is circular, the adapter is cylindrical; if the conductor is flatter, the shape of the sleeve deviates from rotational symmetry accordingly. The adapter may also be made of metal, thereby causing the overmold material to “set” more quickly during the overmolding process.