From the
Wiki article :
"Presidential elector candidates are nominated by their state political parties in the summer before the Election Day. Each state provides its own means for the nomination of electors. In some states, such as Oklahoma, the Electors are nominated in primaries the same way that other candidates are nominated. Other states, such as Virginia and North Carolina, nominate electors in party conventions. In Pennsylvania, the campaign committees of the candidates name their candidates for Presidential Elector (an attempt to discourage faithless Electors). All states require the names of all Electors to be filed with the Secretary of State (or equivalent) at least a month prior to election day. However, under the 14th Amendment, persons holding a state or federal office-whether elected or appointed-may not become electors (an error made, but corrected, before both the 2000 and 2004 elections [1])."