"soft wire for binding bales of hay," by 1891, from hay + wire (n.). Adjective meaning "poorly equipped, makeshift" is 1905, American English, from the sense of something only held together with haywire, particularly said to be from use of the stuff in New England lumber camps for jury-rigging and makeshift purposes, so that hay wire outfit became the "contemptuous term for loggers with poor logging equipment" [Bryant, "Logging," 1913]. Its springy, uncontrollable quality led to the sense in go haywire (by 1915).