TM   10-3930-643-20 ELECTRICAL  SYSTEM  TROUBLESHOOTING  AND  MAINTENANCE. 5-8. Instrument    Panel    Troubleshooting. MALFUNCTION TEST OR INSPECTION CORRECTIVE   ACTION p. AIR PRESSURE GAGE DOES NOT OPERATE. Step   1. Check   the   air   pressure   gage   light   bulb. If   the   bulb   is   burned   out,   replace,   refer   to   paragraph   15-2. Step   2. If   brakes   are   functioning   normally   and   the   air   pressure   gage reading   is   low,   replace   gage,   refer   to   paragraph   15-2. 5-65