An electrical connection system for a lighting device for vehicles, for example a headlight or a lamp, the connection system comprising a plurality of electrical contacts carried by a longitudinal edge of a printed circuit board, which printed circuit board being configured to be carried in an integral manner on the outside or inside of a housing of said lighting device, and a plurality of corresponding electrical connectors carried integral with and projecting sideways from a flexible wiring harness; wherein it further comprises a support shaped like a frame and provided with a plurality of seats each configured to accommodate one of said electrical connectors; said seats being arranged in tandem, aligned side by side in series one to the other longitudinally along said support and each one presenting, on the side of a first longitudinal face of said support, respective inlet openings, each inlet opening being configured to receive a respective electrical connector housed in said seat; said seats each presenting, on the side of a second longitudinal face of the support, opposite to the first face, at least one shoulder element facing the inlet opening of the respective seat and configured to receive in contact therewith, according to a transversal direction to said first and second faces (14,16), a first end of a respective electrical connector opposite to a second end thereof configured to electrically and mechanically couple with a said electrical contact; and wherein said support is delimited, between said first and second longitudinal faces (14,16) thereof, by a pair of opposing longitudinal flanks (22,23) transversely delimiting said seats, said first longitudinal flank being provided with a plurality of through openings each disposed in correspondence with a respective seat; said through openings being U-shaped and being open towards the first longitudinal face so as to interrupt a first edge of the first longitudinal flank, said first edge being facing the side of the first longitudinal face and delimiting part of the first longitudinal face; said through openings being configured to receive laterally in a through manner, transversely to said first longitudinal flank, respective branches of said flexible wiring harness extending laterally cantilevering from the same and each being provided, in correspondence to one of its own free ends, with a said electrical connector; said support being made of a synthetic plastic material and comprising: a pair of longitudinal side members constituting said opposite flanks (22,23) and each bounded between a first (25;27) and second longitudinal edges thereof, opposed to each other; and a plurality of substantially rigid cross-members connecting the side members to each other in one piece, said cross-members being obtained substantially flush with the second longitudinal edge of each side member and delimiting with the second longitudinal edges of the side members the said second longitudinal face of the support, so that the latter is provided with a plurality of through windows communicating with said seats; wherein said U-shaped through openings of said first longitudinal flank detach on said first longitudinal flank a plurality of elastically flexible feet extending cantilevered from said first longitudinal face and each arranged between a pair of seats immediately adjacent to each other; said feet each being provided with a first tooth extending in a longitudinal direction within both seats of said pair of seats immediately adjacent to each other and facing said seats; said cross members being shaped in a transverse direction substantially as an asymmetrical S so as to delimit on said second face first longitudinal slits connected with said through windows and each facing one of said first tooth.