Wis. Stat. § 6.03

(1) The following persons shall not be allowed to vote in any election and any attempt to vote shall be rejected: (a) Any person who is incapable of understanding the objective of the elective process or under guardianship pursuant to the order of a court under ch. 880 , except that when a person is under limited guardianship, the court may determine that the person is competent to exercise the right to vote; (b) Any person convicted of treason, felony or bribery, unless the person's right to vote is restored through a pardon or under s. 304.078 (3) .

(3) No person may be denied the right to register to vote or the right to vote by reason that the person is alleged to be incapable of understanding the objective of the elective process unless the person has been so adjudicated in a separate proceeding instituted for that purpose by an elector of the municipality in accordance with the procedures set forth in ch. 880 for determining incompetency. If a determination of incompetency of the person has already been made, or if a determination of limited incompetency has been made which does not include a specific finding that the subject is competent to exercise the right to vote, and a guardian or limited guardian has been appointed as a result of any such determination, then no determination of incapacity of understanding the objective of the elective process is required unless the guardianship is terminated or modified under s. 880.34 .