TM 10-3930-671-24 LAMP CIRCUIT TEST (45 Amp Systems)- With ignition switch  on,  lamp  on,  and  engine  not  running,  connect  a DC voltmeter to Test Point I as shown in  Figure  9.1.    A plus  12.0-12.6  volts  measurement  should  be  noted  on the    DC    voltmeter.        If    you    receive    a    low    voltage measurement at Test Point 1, check battery and terminal connections. Connect  positive  voltmeter  lead  on  one  of  the  AC Tap terminals Test Point 2).  The DC voltmeter should show 30-60 mV.  Repeat this procedure on the other AC Tap  terminal.    If  you  receive  zero  voltage  at  either  AC Tap terminal, replace regulator. Connect positive DC voltmeter lead on Lamp Driver lead (Test  Point  3).    A  measurement  of  100+  mV  should  be noted.  If you obtain a measurement of 100+mV, replace lamp. FIGURE NO. 9.1 SHORTED RECTIFIER DIODE TEST(45 Amp Systems)-    With    ignition    switch    off    and    engine    not running,   connect   a   DC   voltmeter   to   Test   Point   1   as shown in Figure 9.2. A plus 12.0-12.6 volts measurement  should  be  noted  on  the  DC  voltmeter.    If you receive a low voltage measurement at Test Point 1, check battery and terminal connections. Connect  positive  voltmeter  lead  on  one  of  the  AC Tap  terminals  (Test  Point  2).    The  DC  voltmeter  should not  show  any  voltage.    Repeat  this  procedure  on  the other  AC  Tap  terminal.    Any  voltage  at  either  AC  Tap terminal indicates a shorted positive rectifier diode in the alternator.  Repair alternator. FIGURE NO.  9.2 F-277