TM 10-3930-664-10 KEY CONTROL OR INDICATOR FUNCTION 3 Ammeter Operates  when  ignition  switch  is  ON.    Indicates  if  alternator  operation  is normal.  Needle should indicate in the positive (green) zone when the engine is running above idle. CAUTION 4 Transmission Oil Temperature Operates   when   ignition   switch   is   ON.      Indicates   temperature   of   Gauge transmission oil.  Normal operating temperature for transmission oil is 150° - 240° F (71° -115° C). 5 Fuel Gauge Operates when ignition switch is ON.  Indicates amount of fuel remaining in the tank. Operation   of   the   transmission   at   temperatures   above   250°   F(121°   C)(red   zone   on   gauge)   will   cause damage  to  transmission  parts  and  result  in  transmission  failure.    If  transmission  oil  temperature  exceeds 250° F (121° C), stop the engine and find the cause. 2-8