The invention relates to a method of locating an electrical defect in an underwater electrical distribution modular system (S) comprising a power line (L) along which are disposed:-a line head module (M20) comprising an isolator (22)-a line termination module (M40);-optionally, one or more intermediate modules (M30);-a set of electrical connectors (C1-C4) linkable under the water; the method comprising the following steps after opening of the isolator of the head module following the detection of an electrical defect downstream on the line: -disconnection, by a remotely operated underwater vehicle, of the male connector and of the female connector ensuring the electrical connection between two underwater modules; -fitting of a dielectric stopper on the male connector disconnected from the female connector by a remotely operated underwater vehicle; -closure of the isolator of the head module; -verification of a detection of a defect on the line downstream of the isolator of the head module.