Electoral College: Instructions to State Officials, Responsibilities of the States in the Presidential Election [open pdf - 396KB]
"The United States Constitution and Federal law do not prescribe the method of appointment other than requiring that electors must be appointed on the Tuesday after the first Monday in November (November 8, 2016). In most States, the political parties nominate slates of electors at State conventions or central committee meetings. Then the citizens of each State appoint the electors by popular vote in the state-wide general election. However, State laws on the appointment of electors may vary. Under the Constitution, State legislatures have broad powers to direct the process for selecting electors, with one exception: Article II, section 1, clause 2 provides that 'no Senator, Representative, or Person holding an Office of Trust or Profit under the United States' may be appointed as an elector. It is not settled as to whether this restriction extends to all Federal officials regardless of their level of authority or the capacity in which they serve, but we advise the States that the restriction could disqualify any person who holds a Federal government job from serving as an elector."
Government Printing Office: http://www.gpo.gov/