A method of locating an electrical defect in an underwater electrical distribution modular system including a power line along which are disposed: a line head module including an isolator; a line termination module; optionally, one or more intermediate modules; a set of electrical connectors linkable under the water. The method includes, after opening the isolator of the head module following detection of an electrical defect downstream on the line: disconnection, by a remotely operated underwater vehicle, of a male connector and female connector ensuring electrical connection between two underwater modules; fitting a dielectric stopper on the male connector disconnected from the female connector by a remotely operated underwater vehicle; closing the isolator of the head module; and verification of a detection of a defect on the line downstream of the isolator of the head module.