Wisconsin Statutes Vehicles (Ch. 340 to 351) § 347.20. Lamp or flag on projecting load or fixture

(1) No person shall operate on a highway during hours of darkness any vehicle with a load or fixture thereon extending more than 4 feet beyond the rear of the bed or body thereof unless there is displayed at the extreme rear end of the load or fixture a red light or lantern plainly visible from a distance of at least 500 feet to the sides and rear. The red light or lantern shall be in addition to any tail lamp or clearance lamp which the vehicle is required to carry.

(2) No person shall operate on a highway, at times other than hours of darkness, any vehicle with a load or fixture thereon extending more than 4 feet beyond the rear of the bed or body thereof unless there is displayed at the extreme rear end of such load or fixture a red flag or cloth not less than 12 inches square and so hung that the entire area is visible to the operator of a vehicle approaching from the rear.

(3) This section does not apply to vehicles loaded with loose hay or straw.