Salvadorans living outside of El Salvador can now enroll to vote in the 2014 elections. To be able to vote, an ex-pat from El Salvador will need a national identity document (DUI) with his or her foreign address outside of El Salvador. With that DUI, you can go to the website of the Supreme Electoral Tribunal where there is a form to register to vote in this manner.
With two million or more Salvadorans living outside of the country, the vote from the exterior could be a major wild card. (I don't think any of the polls published in recent months in El Salvador make any attempt to include them). While I do not have the statistics on how many DUIs have been issued with foreign addresses, I have my doubts that we will see more than 100,000 votes from outside of the country. In the 2009 elections, which was the first time that Salvadorans living outside of the country could vote if they returned to El Salvador to cast a ballot, the number of voters was much less than forecast. Of course, the cost of an airline ticket is much less than the cost of the new process of voting from abroad.