3. Is there a ban on corporate donations to political parties?

Source: Article 63, paragraph 1, Political Parties Act 2013.

Artículo 63.- Los partidos políticos podrán recibir financiamiento privado, proveniente de personas naturales o jurídicas, dentro de los límites y con arreglo a los requisitos y condiciones establecidas en la presente Ley,

Article 63.- Political parties may receive private funding from individuals or legal entities, within the limits and in accordance with the requirements and conditions established in this Law.

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

Political parties may receive funding from individuals or legal entities.
Contributions from companies may be in cash or in kind.