求翻译：13． 连接开关、螺口灯具导线时，相线应先接开关，开关引出的相线应接在灯中心的端子上，零线应接在螺纹的端于上。是什么意思？

13. When connecting to the switch, screw lamp wire, that line should be connected switches, switch leads to phase line yingjie in lights on the center of the Terminal, yingjie in the end of a thread in the zero line.