TM  10-3930-638-24&P 2-23.   HORN   AND   BACK-UP   ALARM   SYSTEM   TROUBLESHOOTING MALFUNCTION TEST OR INSPECTION CORRECTIVE  ACTION 1. HORN DOES NOT SOUND Step 1. Disconnect positive wire from side of horn. Connect positive voltmeter lead to connector on positive  wire,  and  negative  voltmeter  lead  to vehicle  ground. a. If voltmeter indicates 24 Vdc, reconnect positive wire to side of horn and proceed to step 2. b. If voltmeter does not indicate 24 Vdc, troubleshoot  25  ampere  circuit  breaker (para 2-21, malfunction entry 2, step 6). If 25 ampere circuit breaker test is satisfactory, check for open circuit in wiring  between  battery  positive  post  and connector on horn positive wire. Step 2. Disconnect horn button wire from bottom of horn. Temporarily connect jumper wire from terminal on bottom of horn to vehicle ground. a. If horn sounds, reconnect horn button wire to bottom of horn and proceed to step 3. b. If horn does not sound, replace horn (para 2-32a). Step 3. Disconnect horn button wire from  terminal  on  steering column. Temporarily connect jumper wire from connector on horn button wire to vehicle ground. a. If horn does not sound, check for open circuit in wire between steering column and horn. b. If horn sounds, replace horn  switch  (para  2-32b). 2-105