TM 10-3930-69-20 15.  HORN DOES NOT OPERATE (CONT). KNOWN INFO 24 vdc circuits operate. Fuse 5 OK. POSSIBLE PROBLEMS Wire 27 faulty. Horn faulty. Horn contact plate faulty. Wire 21 faulty. KNOWN INFO 24 vdc circuits operate. Fuse 5 OK. Wire 27 OK. POSSIBLE PROBLEMS Horn faulty. Horn contact plate faulty. Wire 21 faulty. TEST OPTIONS Voltage test. STEACE-R #89. REASON FOR QUESTION This question eliminates a possible problem or group of possible problems determining where troubleshooting continues. TEST OPTIONS Continuity test. STE/ICE-R #91. REASON FOR QUESTION If continuity is not present, fault is ground circuit.  If continuity is present, horn is faulty. 2-208