Voters must write in the name and register the vote by making a mark in the ballot in the appropriate space selecting the write-in option. Otherwise, the vote will likely not be counted.
A write-in candidate for president must have each of the presidential electors file a declaration of write-in candidacy with the secretary of state no later than 14 days before the election.
(California Elections Code Ann. §§ 338,5001, 5100, 6901,7100, 7110, 7300, 7578, 7843, 8303, 8304, 8400, 8403(a)(2), 8451, 8550, 8650, 8651, 8652, 8653)
Any group of individuals, equal in number to the number of presidential electors to which this state is entitled, who desire to be write-in candidates for presidential electors pledged to a particular candidate for President and Vice President of the United States shall file a declaration of write-in candidacy.References: Write-in candidates, California