Safety locking structure to prevent unintentional disconnection of a mating pair of male and female electrical connectors. The locking structure comprises a hollow tubular shell and a U-shaped clevis pin having a base portion and a pair of legs. The mating end of a first one of the electrical connectors is insertable into the shell from one end thereof and is captively held therein. The other end of the shell is provided with two pairs of aligned holes, each pair being adapted to receive a leg of the U-shaped clevis pin with a portion of each clevis pin leg extending into the interior of the shell. The mating end of the second one of the connectors is insertable into the shell from the other end thereof and into mating relationship with the first connector. The mating end of the second connector is provided with an exterior annular clevis pin locking groove which, when the connectors are fully mated, receives the above noted portions of the clevis pin legs to lock the second connector in mated relationship with the first connector. The shell may be configured to captively mount the first connector to a panel or to make an in-line connection between a mating pair of male and female connectors, the first of the connectors being captively mounted in the shell in the same manner described with respect to the second connector.