16. Is there a limit on the amount a donor can contribute to a political party during an election?

Source: Articles 65 and 66, Political Parties Act 2013.

Artículo 65.- Los partidos políticos podrán recibir aportaciones económicas individuales de personas naturales o jurídicas, en un mismo año fiscal, hasta el dos por ciento del presupuesto del año anterior, aprobado por la Asamblea Legislativa al Tribunal Supremo Electoral.

Artículo 66.- Los partidos políticos, en el año anterior a cualquier elección, podrán recibir aportaciones económicas individuales de personas naturales o jurídicas en un mismo año fiscal, hasta el tres punto cinco por ciento del presupuesto especial extraordinario de elecciones, aprobado por la Asamblea Legislativa al Tribunal Supremo Electoral, en la elección anterior del mismo tipo.

Article 65.- Political parties may receive individual financial contributions from natural or legal persons, in the same fiscal year, up to two percent of the previous year's budget, approved by the Legislative Assembly to the Supreme Electoral Tribunal.

Article 66.- In the year prior to any election, political parties may receive individual financial contributions from individuals or legal entities in the same fiscal year, up to three point five percent of the special extraordinary election budget approved by the Legislative Assembly for the Supreme Electoral Tribunal in the previous election of the same type.

Ley de Partidos: https://www.asamblea.gob.sv/sites/default/files/documents/decretos/2E597B83-D1C9-4C91-A9C9-6EC8A44FBA0F.pdf  

-The Political Parties Act has a loophole, as it only sets limits during ordinary and pre-election periods, but not a maximum limit per donation in an election year.
In a pre-election year, the limit is the special extraordinary election budget of the previous election of the same type in USD.

-In practice, for election years, the Supreme Electoral Tribunal has set a limit of 3.5 percent of the special extraordinary election budget for the previous election of the same type.