This article presents the hybridization of a multiconductor transmission line (MTL) solver with the circuit solver ngspice to treat the terminations and interconnections of transmission lines. The MTL solver is implemented using the finitedifference time-domain technique (FDTD). Transient analysis and crosstalk in multiconductor transmission lines has been widely studied but the line terminations and the connections between lines are mostly restricted to lumped RLC components. However, realistic systems such as power distribution or communication systems have complex and a priori unknown connections. Interfacing with a circuit solver opens the possibility of including in the MTL simulation any component for which a netlist can be written or already exists, i.e dispersive elements, such as ferrites, and electronic components such as diodes, amplifiers or transistors. This flexibility allows to simulate networks of MTLs terminated in and connected by arbitrary circuits. The proposed method is validated comparing against laboratory measurements.