Texas Election Code - ELEC § 192.103. Presiding Officer;  Elector Vacancy

(a) The secretary of state shall preside at the meeting of electors described in Section 192.104.

(b) The position of an elector is vacant if the elector has failed to execute the oath under Section 192.102.

(c) The secretary of state shall fill a vacancy with a substitute elector nominated in accordance with political party rules or named by an independent or write-in candidate for president, as applicable.  A substitute elector who is filling the position of an elector is considered an elector for purposes of this chapter.  If a person's position as elector is determined to be vacant, the person may not serve as a substitute elector with respect to that meeting of electors.

(d) To qualify as a substitute elector under Subsection (c), an individual who has not executed the oath required under Section 192.102 shall execute the following oath:  “I swear to serve and to mark my ballots for president and vice president consistent with the oath of the individual to whose elector position I have succeeded.”