Abstract: A system for transmitting operational control messages to a plurality of remotely-disposed cable-locating transmitters uses a spare communication line associated with each transmitter to carry the control messages from unit to unit. In the case of a fiber optic cable, the control message is transferred from an incoming telephone line associated with a first cable-locating transmitter to a spare optical fiber. The control message then propagates down the fiber to the next transmitter (where this transmitter does not otherwise have accessibility to a telephone line). This transmitter converts the optical signal to an electrical signal and either uses the control message (if indeed destined for that particular transmitter), or re-converts it to optical form and sends it further along the spare fiber to the next remote cable-locating transmitter further down the line.