TM  10-3930-638-24&P 2-23.   HORN   AND   BACK-UP   ALARM   SYSTEM   TROUBLESHOOTING   (cont) MALFUNCTION TEST OR INSPECTION CORRECTIVE  ACTION 2. BACK-UP ALARM DOES NOT SOUND Step 1. Turn IGNITION switch key to ON position and temporarily connect a jumper wire to terminals of back-up  alarm  switch. a.  If  back-up  alarm  sounds,  replace  back-up alarm  switch  (para  2-31b). b. If back-up alarm does not sound, proceed to step 2. Step 2. Disconnect wire from positive terminals of back-up alarm. Temporarily connect a jumper wire between positive battery cable and positive terminal of back-up alarm. a. If back-up alarm sounds, reconnect wire to positive alarm terminal and proceed to step 3. b. If back-up alarm does not sound, connect a jumper wire to vehicle ground and back-up alarm  negative  terminal.  If  alarm  does  not sound with ground jumper at negative terminal and battery positive jumper at positive  terminal,  replace  back-up  alarm (para  2-32c). Step 3. Turn and hold IGNITION switch key at LAMP TEST position. a. If at least one warning indicator (TRANSMISSION TEMPERATURE, HYDRAULIC FILTER, or ENGINE TEMPERATURE) is on, check for open circuit in wiring between back-up alarm, back-up alarm switch, and 6 ampere circuit breaker. b. If at least one warning indicator is not on, turn IGNITION switch key to ON position and check if a slight buzz can be heard at electric fuel pump. If slight buzz indicating electric fuel pump operation is not heard, troubleshoot IGNITION switch (para 2-25). If slight buzz is heard, troubleshoot  warning  indicators  (para  2-25). NOTE If flood lights, tail lights, stop lights and gage lights are all inoperative, turn IGNITION switch key to OFF position. Connect positive voltmeter lead to terminal F of VEHICLE LIGHTS switch cable connector and negative voltmeter lead to vehicle ground. If voltmeter does not indicate 24 Vdc with IGNITION switch key set at ON position, check for open circuit in wiring between terminal F of cable connector and IGNITION switch. If wiring check is satisfactory, replace IGNITION switch (para 2-28c). 2-106