The break-arm you see atop the crossarm in the foregraound provided the street series path for the street light shown and others like it within its loop. One wire went down to the fixture (lamp) and the other returned up to the other side of the break-arm...in electrical series. Basically street series systems operate like a string of miniature holiday lights. When a series lamp burns out, fails or is being replaced, the remainder remain lit owing to an automatic bypass in the socket or lamp. Los Angeles and many other communities with the LA basin still have many series street lighting systems still in use. Some are older, historic and original incandescent lights while others are more modern ones using series transformers within their fixtures within the same series loops. An automatic photoelectric controller for each "loop" controls their dusk-to-dawn operation. Added note: A close view of this original photograph notes double-groove or transposition insulators were used on the ends of each break-arm pin to double-up dead-end strength of each wire (thus, it looks like there is connection between the two break-arm insulators, fyi).