TM   9-2320-273-20 Table  5-6.  Warning  Lamps  and  Alarms  Circuit  Troubleshooting  (Continued). INSTRUCTION INDICATION YES NO REMARKS 3 LOW   AIR   PRESSURE   WARNING   LAMP   AND/OR   BUZZER   INOPERATIVE   (Continued). c.  Buzzer  only  works. Replace  the bulb  (para 5-61). d.  Neither  lamp  nor Trouble- buzzer  operates. shoot   wiring (refer  to schematic  in Appendix   D). 4 BACKUP   ALARM   IS   INOPERATIVE. NOTE The compressed air system must be within normal operating pressures to actuate the backup switch. 1 Verify   the   backup alarm  override  switch is OFF, and the EN- GINE  RUN  switch  is ON.   Place   the   ratio selector  in  one  of  the reverse  gears. 2 Check  for  voltage  at 12  dc  volts  nominal. Go to Step Go to Step the  alarm  with  a 3. 4. multi  meter. 3 Check ground at Bad ground. Repair Replace the alarm  for  loose  or ground. alarm (para dirty   ground. 5-78). 4 Attach a test lead Alarm  operates. Replace Go  to  Step across the terminals backup 5. on  the  backup  switch. switch  (para 5-77). / 5 ‘  Attach  a  test  lead Alarm  operates. Replace Go to Step across the terminals switch. 6. on  the  override switch, 6 Troubleshoot    wiring through   circuit breaker.  Refer  to schematic  in Appendix   D. 5-39