The governor and lieutenant governor shall be elected upon a joint ballot by the qualified electors of the state beginning with elections held in 1976. A single vote shall be cast upon a joint ballot by each qualified elector for the joint candidates representing the political party or affiliation of his choice. The joint candidates having the highest number of votes shall be declared elected, but if two or more joint candidates shall have an equal and highest number of votes for governor and lieutenant governor, the two houses of the legislative assembly at its next regular session shall forthwith in joint session choose one pair of such joint candidates for said offices. The returns of the election for governor and lieutenant governor shall be made in such manner as shall be prescribed by law.