Twelfth Amendment did not change the composition of the Electoral College or the duties of the electors, it did change the process whereby a President and a Vice President are elected. The new electoral process was first used for the 1804 election.
The Twelfth Amendment cannot be understood outside of the Electoral College, which was set out in the 1787 Constitution as the mechanism by which Americans select their presidents. There were four crucial aspects of that mechanism.  Stipulations of the Twelfth Amendment. The Twelfth Amendment did not change the composition of the Electoral College, but did change the process whereby a President and Vice President were elected. Before the adoption of the Twelfth Amendment, the Electoral College stated that each elector could cast two votes; each elector was not permitted to vote for two people whom are a part of the same state as that elector. The Twelfth Amendment sets out the procedures for the election of the President and Vice President: Electors cast one vote for each office in their respective states, and the candidate having the majority of votes cast for a particular office is elected. 1 Tadahisa Kuroda, The Origins of the Twelfth Amendment: The Electoral College in the Early Republic, 1787a€“1787â (1804). 2  1994 David. P, Currie The constitution In: Congress The, jeffersonians€“1801a (1801â). 3  1829 2001 & William Josephson. Beverly, J ross Repairing The, electoral College. 22.  j legis The person receiving a majority of the votes of electors becomes the president. In the event that no candidate receives a majority of electoral votes, the decision falls, under the 12th Amendment, to the House of Representatives. Pages carry into the Senate electoral votes for 1948 election.  The Twelfth Amendment refined the process whereby a President and a Vice President are elected by the Electoral College. The amendment was proposed by the Congress on December 9, 1803, and was ratified by the requisite three–fourths of state legislatures on June 15, 1804. If no candidate for Vice President has a majority of the total votes, the Senate, with each Senator having one vote, chooses the Vice President. The Twelfth Amendment requires the Senate to choose between the candidates with the two highest numbers of electoral votes. The Twelfth Amendment (Amendment XII) to the United States Constitution provides the procedure for electing the President and Vice President. It replaced Article II, Section 1, Clause 3, which provided the original procedure by which the Electoral College functioned. If no candidate for Vice President has a majority of the total votes, the Senate, with each Senator having one vote, chooses the Vice President. The Twelfth Amendment requires the Senate to choose between the candidates with the two highest numbers of electoral votes. U.S Territories are not represented in the Electoral College The12th amendment provides for each elector to cast one vote for President and one vote for Vice President. It also specifies how a President and Vice President are elected. The 12th Amendment (ratified on June 15, 1804) changed the method  that determines how the US Vice President is chosen. Previously,  the electoral college Presidential candi … date with the  second-highest number of electoral votes became the Electoral College under the Twelfth Amendment [edit]. While the Twelfth Amendment did not change the composition of the Electoral College or the duties of the electors, it did change the process whereby a President and a Vice President are elected. The new electoral process was first used for the 1804 election. If no candidate for Vice President has a majority of the total votes, the Senate, with each Senator having one vote, chooses the Vice President. The Twelfth Amendment requires the Senate to choose between the candidates with the two highest numbers of electoral votes.
http://constitutioncenter.org/interactive-constitution/amendments/amendment-xii http://constitution.laws.com/12th-amendment http://www.heritage.org/constitution#!/amendments/12/essays/165/electoral-college http://law2.umkc.edu/faculty/projects/ftrials/conlaw/electoralcoll.htm https://en.wikipedia.org/wiki/Twelfth_Amendment_to_the_United_States_Constitution https://en.wikipedia.org/wiki/Twelfth_Amendment_to_the_United_States_Constitution http://www.answers.com/Q/How_did_the_twelfth_amendment_change_the_electoral_process https://en.wikipedia.org/wiki/Twelfth_Amendment_to_the_United_States_Constitution
how did the twelfth amendment change the electoral college?