S-SERIES INSTRUMENTS magnetic field produced by the "hot" coil is negligible.  At this  time  the  pointer  and  armature  assembly  will  align itself  with  the  resultant  magnetic  field  produced  by  the "cold"  and  bucking  coils  at  the  1  00°F  position.    The mag-netic field of the "cold" and bucking coils is always a constant and serves as a reference.  As the temperature of   the   liquid   increases,   the   resistance   of   the   sender decreases since the thermistor has a negative tempera- ture  coefficient.    The  decrease  in  sender  resistance  in- creases  the  current  flowing  in  the  "hot"  coil,  reaching  a maximum at the full-scale position.  Thus, the interaction of   the   magnetic   fields   of   the   three   coils   produces   a resultant  magnetic  field  which  controls  the  rotation  and position of the armature and pointer assembly. NOTE  -  The  gauge  is  grounded  to  chassis  through the ground terminal when plugged into the Instrument cluster printed circuit. Figure 19 - Water Temperature Gauge Circuit Diagram The  sender  terminal  is  the  first  terminal  clockwise  from ground  terminal  (when  viewed  from  back  side).    The ignition terminal is directly opposite from sender terminal. Testing 1. Disconnect   sender   wire   from   water   temperature sender unit. 2. Connect  one  lead  of  gauge  tester  to  sender  wire. Connect   other   lead   of   tester   to   a   good   vehicle ground.    (Gauge  tester  now  substitutes  for  sender unit. 3. Turn  key  switch  "ON"  (Be  sure  there  is  power  to cluster. 4. Set tester: For 260° gauges, use 55 ohms.  For 2200 gauges,  use  99  ohms.    Temperature  gauge  should read  at  full  scale  (HOT).    (Pointer  within  2  pointer widths of hash mark. 5. Set  tester:  For  2600  gauges,  use  113  ohms.    For 2200 gauges, use 212 ohms.  Gauge should read at half  scale.    (Pointer  within  2  pointer  widths  of  hash mark. 6. Set tester to 1365 ohms   Gauge  should  read  at  low scale  (COLD).    (Pointer  within  2  pointer  widths  of hash mark. If temperature gauge responds correctly to various tester settings,  gauge  and  wiring  between  gauge  and  sender unit are OK..  Trouble is in sender unit or sender unit is not grounded. NOTE  -  Sealant  or  dirt  on  threads  of  sender  unit  or engine  cylinder  head  may  prevent  a  good  electrical ground    Check   for   this   condition   before   replacing sender unit. If gauge does not respond to tester: a. Check continuity of gauge wiring circuits.  Make sure connectors' terminals are clean and tight. b. Check gauge cluster ground circuit.  Make sure circuit is grounded. c. If wiring is OK, replace gauge. A similar procedure is used to test engine, transmission and rear axle oil temperature gauges.  Refer to Table 1 for tester settings. AUXILIARY TEMPERATURE GAUGES The   auxiliary   (optional)   temperature   gauges   are   also electromagnetic type and are actuated by  sending  units (variable   resistance   thermistors).      Sending   units   are located    in    the    component    on    which    temperature monitoring   is   desired   (engine   oil,   transmission,   rear axles,  etc.    Operating  principles  and  testing  of  auxiliary tempera-ture gauges are similar to the water temperature gauge previously described.  Refer to Table 1    for    tester    settings    for    checking    these    gauges. CTS-4140Y - Page 11