If a complaint is lodged regarding an unlawful search of a personal vehicle, which Constitutional amendment is relevant?

The relevance of the 4th Amendment to a complaint about an unlawful search of a personal vehicle lies in its protection against unreasonable searches and seizures. This amendment establishes that citizens have the right to secure their persons, houses, papers, and effects against arbitrary governmental intrusion. When an individual believes that their vehicle was searched without probable cause or a warrant, the 4th Amendment's provisions come into play, as it directly addresses issues of privacy and personal freedom regarding searches.

In contrast, the 1st Amendment focuses on the freedoms of speech, religion, press, assembly, and petition, which do not apply to the context of a vehicle search. The 5th Amendment deals with the right against self-incrimination and due process, while the 14th Amendment provides for equal protection under the law and due process clauses regarding state actions. Therefore, none of these amendments are pertinent to the issue of unlawful searches in a way that the 4th Amendment is. This makes the 4th Amendment the most appropriate answer when discussing the legal underpinnings of search and seizure policies.