TM 10-3930-671-24 Volt Drop Tests  3 The   objective   of   volt   drop   tests   is   to   check   circuit resistances of wiring and starter motor circuit in order to locate trouble spots. 1. Check  voltage  drops  with  engine  cranking. The procedure is to look at resistance in terms of the  voltage  drop  across  a  portion  of  the  circuit while the engine is being cranked. For safety when checking or removing battery connections, always  first  disconnect  the  negative battery   cable   at   the   engine   ground connection. NOTE • The following tests assume that the engine is in good operating condition and  the  battery  is  at  or  close  to  full charge. • Rule of thumb formula for measuring  voltage  drops:  Maximum circuit   voltage   drop-   0.20   volts   per 100 amps. 2.    Prevent engine from starting when cranking. Disconnect  the  fuel  shut-off  solenoid  so  the  engine  will not start. Never operate the starter motor more than  30  seconds  at  a  time  without pausing to allow it to cool for at least 2  minutes.    Overheating  caused  by excessive    cranking    will    seriously damage the starter motor. 3.    Crank engine and read voltage a) Check   battery   positive   cable   and   connections. Connect a voltmeter from the positive (+) battery terminal  to  the  "Battery"  terminal  on  the  starter solenoid.    With  the  voltmeter  set  on  its  lowest scale,   crank   the   engine   for   15   seconds,   and measure the voltage.  A reading higher than 0.4 volts indicates high resistance.  Check the cable for   loose   connections   or   the   battery   terminal connection for corrosion. b) To check positive post battery terminal connection,  connect  voltmeter  from  the  battery post to the terminal on cable.  Crank the engine. A voltage reading above 0 volts indicates a poor connection.    Clean  the  terminal  post  and  cable end.  Tighten bolt. F-303