TM 10-3930-671-24 DO NOT, disconnect the altemator output lead from the altemator  while  the  alternator  is  operating,  as  damping effect of the battery will be lost.  The  voltage  will  rise  to an    extreme    value    and    permanent    damage    to    the alternator will occur. DO NOT, remove the altemator from vehicle without first disconnecting the grounded battery cable. ELECTRICAL TEST PROCEDURE PREUMINARY INSPECTION - Prior to electrical testing, a   thorough   visual   inspection   is   required   to   eliminate associated   conditions   that   may   be   interpreted   as    a defective alternator or voltage regulator. Check  all  electrical  leads  and  connections.    Repair  or replace necessary parts.  Check alternator drive belt and pulleys.  Severe operating conditions will accelerate belt and pulley wear.  Tighten belt to avoid slippage. Check   alternator   brushes   for   wear.      Replace   if   worn more  then  half  their  original  length.    While  the  brush cavity is exposed, check and clean slip rings, if required. Use a fine grade of crocus cloth. Inspect   filter   (radio)   capacitors   for   possible   open   or shorted components, when used. The  battery  used  in  electrical  testing  must  be  of  correct voltage and must be in good condition, and fully charged. lf  a  slave  or  jumper  battery  is  used  in  testing,  it  should meet  all  requirements  and  must  be  securely  connected to avoid accidental loss of connection, observe polarity. IN-VEHICLE ALTERNATOR SYSTEM TEST Test Equipment Requirements:  Volt ampere tester, such as  Sun  Electric  Model  VAT20,  or  equivalent,  with  meter ranges as shown below. 1. DC  ammeter  0  -  150  amp  scale  and  0-5  amp field current 2. AC/DC voltmeter - 0 - 20 Volts Scale 3. Rheostat    -    50    ohms,    100    watts,    1/4    Ohm Resistor 4. Carbon  pile  -  600  amp,  such  as  Sun  BST-6,  or equivalent 5. In-circuit   diode   tester,   such   as   Sun   RDT   or equivalent. 6. Test lamp - 12 Volt DC. 7. Ohmmeter - Any commercial type The  alternator  service  technician  is  required  to  test  the charging  system  on  the  vehicle,  or  to  ’bench  test",  the components to determine if disassembly and repairs are needed. It  is  impossible  to  include  accurate  and  complete  wiring diagrams of all vehicles using the "TA" alternator system. Certain  general  circuits,  essential  and  common  for  all applications, are listed. All   grounds   are   labeled   as   GND,   or   with   the   ground symbol,   and   are   considered   ’NEGATIVE",   (NEG)   (-) where the insulated or ungrounded circuit is "POSITIVE", (POS.) (+). The  panel  ammeter  shown  in  test  circuit  diagrams  may not   exist   in   certain   vehicles,   in   such   instances,   the ammeter circuit becomes a simple conductor. The charge indicator lamp, shown in test circuit diagrams may be eliminated in favor of a  75  ohm  resistor,  one  or the   other   is   required   to   provide   controlled   alternator excitation at low rotor speed. The key type ignition switch  in  our  diagrams  may  be  an oil pressure switch, or some other  control,  however,  the function remains the same, to switch alternator excitation current "on and off,.  The switch must be in good working order. F-275