Abstract: A flat flame-retardant harness system includes: a conductor including a plurality of connection contacts, a first position provided with a connector and a second position provided with a temperature sensor, and a wiring pattern for electrically connecting the plurality of connection contacts and the second position to the first position; a lower non-combustible layer provided to contact a lower portion of the conductor, having a plurality of first bus bar coupling portions having first holes formed at positions corresponding to the plurality of connection contacts, and including a flame-retardant material; and an upper non-combustible layer provided to contact the upper portion of the conductor, having a plurality of second bus bar coupling portions having second holes formed at positions corresponding to the plurality of connection contacts, and including a flame-retardant material, wherein each connection contact contacts a bus bar by a first means, and thus is electrically connected.