The optical properties of T-shaped GaAs/AlGaAs quantum wire (QWR) waveguide structures are studied with a magnetic field oriented parallel or perpendicular to the QWR axis. The QWRs were fabricated by the cleaved edge overgrowth (CEO) technique. At low values of the magnetic field oriented perpendicular to the QWR axis, a strong increase in the light emission intensity is observed for all injection currents. For the magnetic field direction parallel to the QWR axis a completely different behavior is found. For magnetic fields greater than 4 T a decrease in the intensity of the emitted light for injection currents below 0.125 mA is observed, while an increase is measured for injection currents larger than 0.125 mA. The origin of the effects induced by the magnetic field is interpreted in terms of optical properties of a one-dimensional (1D) system.