TM 10-3930-671-24 2. Trouble  in  the  charging  system  will  show  up  as one or more of the following conditions: A. Abnormal charge indicator lamp operation. B. Abnormal charging system operation. A. Abnormal Charge Indicator Lamp Operation Check the indicator lamp for normal operation as shown below. Ignition Switch Lamp Engine OFF OFF STOPPED ON ON STOPPED ON OFF RUNNING If     the     (ammeter)     charge     indicator     lamp     operates normally,  proceed   to   "B.      Abnormal   Charging   System Operation".    Otherwise,  proceed  to  one  of  the  following three abnormal conditions. 1. Switch  Off,  Lamp  On.    In  this  case,  disconnect the two leads from the generator No.  1 and No. 2 terminals.  If the lamp stays on, there is a short between these two leads.  If the lamp goes out, replace  the  rectifier  bridge.    This  condition  will cause  an  undercharged  battery.    Remove  and repair the altemator. 2. Switch   On,   Lamp   Off,   Engine   Stopped.      This condition can be caused by the defects listed  in Item  1  above,  or  by  an  open  in  the  circuit.    To determine   where   an   open   exists,   proceed   as follows: a. Check for a blown fuse, a burned-out bulb, defective bulb socket, or an open in No.  1 lead circuit between alternator and ignition switch. b. If no defects have been found, proceed to "B. Abnormal Charging System Operation". 3. Switch  On,  Lamp  On,  Engine  Running.    Check for   a   blown   fuse   between   indicator   lamp   and ignition switch.  The other possible causes of this condition are covered in "B.  Abnormal Charging System Operation" section. If a defect has been found and corrected at this point, no further checks need be made. B. Abnormal Charging System Operation 1. Be sure that an undercharged condition (discharged   battery)   has   not   been   caused   by ignition  key  switch  or  other  accessories  having been left on for extended periods. 2. Check  the  alternator  drive  belt  for  damage  and proper tension. 3. If a battery defect is suspected, check condition of the battery. 4. Inspect    the    wiring    for    defects.        Check    all connections for tightness and cleanliness, including   the   connectors   at   the   alternator   and connections at the battery. 5. With  ignition  switch  ON  and  all  wiring  harness leads connected, connect a voltmeter from: a. Alternator BAT terminal to ground. b. Alternator No.  1 terminal to ground. c. Altemator No.  2 terminal to ground. A   zero   reading   indicates   an   open   between voltmeter  connection  and  battery.    Repair  as required. 6. With    all    accessories    turned    off,    connect    a voltmeter across the battery.  Operate engine at moderate  speed  (1500-1800  rpm).    If  voltage  is 15.5   volts   or   more   (12-volt   system),   remove alternator for repair. 7. If  previous  Steps  1  thru  6  check  satisfactorily, check alternator as follows: a. Disconnect battery ground cable. b. Connect  an  ammeter  in  the  circuit  at  the BAT terminal of the alternator. c. Reconnect battery ground cable. d. Connect  a  carbon  pile  across  the  battery. Turn on all accessories. e. Disconnect ignition coil.  Crank engine for 15 seconds with coil disconnected. Connect   coil.   Start   engine   and   operate engine  at  max  no-load  governed   speed. Adjust  carbon  pile  as   required   to   obtain maximum current output. Ammeter should read within 10 amps of rating. f. If ampere output is within 10 amps of rated output   as   stamped   on   alternator   frame, alternator    most    likely    is    not    defective. Recheck Steps 1 thru 6. IMPORTANT   -   If   output   in   amperes   is   correct,   but charge   indicator   lamp   stays   on,   check   diode   trio   and rectifier bridge. F-263