Wis. Stat. § 342.41: Identity of buyer.

(1) Notwithstanding s. 342.15, after December 31, 2015, no individual may sell a motor vehicle to another individual, including transferring a junk vehicle by bill of sale, unless within 30 days of the sale the seller reports to the department the identification number of the vehicle and the identity of the individual buyer.

(2) The department shall accept electronically information related to the sale of the motor vehicle, including all of the information required to be reported under sub. (1).