Check the wiring at the suspect circuit for voltage and ground. Brown wire is tail-lamp voltage, Yellow wire is voltage for turn/brake, your lower brake lites and turn use the same bulb filament, just not at the same time. Black wire is ground. Turn on the key, turn on, left turn, check for oltage at yellow wire, if no voltage, backtrack the circuit, goes to multifunction switch. If the brake lites work on that side and turn doesn't, suspect the multifunction switch.