A leadless type ballast transformer having a connector at one end of the housing for accepting a mating connector which supplies voltage to the ballast and provides the operating voltage to the lamps controlled by the ballast. Uninsulated connection leads extending inwardly of the housing from the connector terminals to contact the lugs of a terminal board adjacent a transformer coil with the magnet wires of the transformer coils also being in contact with the terminal board lugs. The connection leads and magnet wires are permanently electrically connected to the terminal board lugs by ultrasonic welding.