Wis. Stat. § 347.28: Certain vehicles to carry flares or other warning devices.

(1) No person shall operate a motor truck or motor bus more than 80 inches in width or a truck tractor or road tractor on any highway outside the corporate limits of a city or village during hours of darkness unless such vehicle carries in a place readily accessible to the driver the following warning devices:

(a) At least 3 pot torches or 3 red electric lanterns or 3 red emergency reflectors, each of which shall be capable of being seen and distinguished at a distance of at least 600 feet under normal atmospheric conditions during hours of darkness. If pot torches are carried in lieu of red electric lanterns, at least 3 red-burning fusees shall be carried in addition to such pot torches; and

(b) At least 2 red-cloth flags, not less than 12 inches square, with standards to support such flags.

(2) No person shall operate upon a highway outside the corporate limits of a city or village during hours of darkness any motor vehicle used for the transportation of explosives or any cargo tank truck used for the transportation of flammable liquids or compressed gases unless there is carried in such vehicle 3 red electric lanterns or 3 red emergency reflectors meeting the requirements of sub. (1). No pot torch or fusee or signal produced by flame shall be carried in any such vehicle. Such red emergency reflectors shall comply with the specifications for such reflectors as set forth in interstate commerce commission motor carrier safety regulations.