The mixed gauge track between Pencader Junction and Carmarthen was "ready" in August 1866 and M&MR goods trains started running through from 1 November 1866. Passenger train operation was delayed because of the difficulty in obtaining Board of Trade approval for passenger operation, which was not received until February 1868. In the meantime, southbound mixed (goods and passenger) M&MR trains detached their passenger coaches at Pencader and re-attached them on the northbound journey., In any case, the M&MR passenger trains ceased running south of Pencader in 1872.