PURPOSE: To insulate a rotary electric machine coil for automobiles having excellent resistance to heat cycle, rain water infiltration and vibration during the running of an automobile by coiling a conductor on an iron core after applying a varnish to the conductor and baking it and forming an enamel coating on the conductor.

CONSTITUTION: A method for insulating a rotary electric coil for automobiles involves coiling, an electric wire, which is insulated by polyimide and manufactured by applying pyromellitic dianhydride-type polyimide varnish to a conductor and baking it plural times, around an iron core while interposing a prescribed slot insulator and an interphase insulator between them and further, if necessary, impregnating the wire with thermal-setting resin and heat- hardening the resin. The enamel coating obtained by the insulating method involving those processes has excellent adhesion strength to the conductor and since alteration of the thermal expansion coefficient depending on the temperature is small in a wide range from room temperature to about 400°C, the enamel coating is durable enough to meet the extreme ups and downs of the conductor's temperature caused by putting on a brake or accelerating an automobile and is hard to peel off of the conductor. Further, since the coating is tough, a crack hardly penetrates the coating even if the crack is formed in the impregnated resin touched by the coating.