Abstract: A method of producing an instrument panel of a motor vehicle or similar molding of forming resin which includes a section for fitting an electrical part. The electrical part fitting section is constituted by a coupler engageable with the electrical part and an opening which is contiguous with the interior of the coupler. The opening is surrounded in a liquid-tight configuration by a pressing member for sealing which is disposed on one of coactive parts of a metal mold. The coupler is removably mounted on the other metal mold part. When the metal mold parts are clamped, a peripheral edge portion of the coupler abuts against a portion of the pressing member which surrounds an opening of the pressing member. A flexible printed circuit to which the electrical part is electrically connectable is interposed between the coupler and the pressing member such that terminal portions of the circuit face the inside of the coupler.