TM 10-3930-671-24 REED   SWITCH   AND   POSITIVE   RECTIFIER   DIODE TEST  (22/30   Amp   Systems)-   With   ignition   switch   off, engine     not     running,     temporarily     disconnect     battery ground  cable  from   battery.      Connect   test   AMMETER, using   0-50   ampere   scale,   between   alternator   output terminal   and   original   output   lead.      Secure   leads   and reconnect battery (Figure No.  9). Connect test VOLTMETER as follows:  negative lead to negative  battery  terminal,  positive  lead  to  points  STA., FLD.      and   OUTPUT,   in   that   order.      With   voltmeter, connect to STA.  then FLD.  in both tests, meters should read  "Zero".    Move  positive  lead  to  OUTPUT  terminal, meter   should   read   battery   voltage   12.0   to   12.6   volts. Ammeter should read "Zero" amperes. If  voltmeter  at  test  point  STA.    indicates  above  "Zero" volts, one of the positive rectifying diodes is shorted. Test  ammeter  will  indicate  current  discharge.    Remove alternator from engine and make necessary repairs. If voltmeter at test point FLD., indicates above zero volts, there is a fault in the regulator allowing the reed switch to remain  closed.    The  test  ammeter  will  indicate  current discharge   and   the   charge   indicator   lamp   may   glow. Replace regulator and retest. FIGURE NO.  9. F-276