TM 1-1510-225-10 2-111 (4)   Pilot's Flight Instrument Lights.   Illumination of the pilot's flight instruments is controlled by a rheostat switch placarded PILOT FLIGHT INSTR BRT  /   OFF,  located  on  the  overhead  control  panel.   The pilot's flight instrument light circuit is protected by a 7-1/2-ampere circuit breaker placarded  COPLT FLT INSTR,  located  on  the  right  sidewall  circuit  breaker panel. (5)   Copilot’s Flight Instrument Lights.   Illumination    of    the    copilot's    flight    instruments    is controlled  by  a  rheostat  switch  placarded   COPILOT FLIGHT INSTR, BRT / OFF, located on the overhead control   panel.      The   copilot's   flight   instrument   light circuit  is  protected  by  a  7-1/2-ampere  circuit  breaker placarded  COPLT  FLT  INSTR,  located  on  the  right side-wall circuit breaker panel. (6)   Avionics Panel Lights.  Illumination of the avionics   panel   is   controlled   by   a   rheostat   s witch placarded   AVIONICS   PANEL   LIGHTS   BRT   /   OFF, located  on  the  overhead  control  panel.    The  avionics panel  light  circuit  is  protected  by  a  5-ampere  circuit breaker placarded   AVIONICS  &  ENG  INSTR, located on the right sidewall circuit breaker panel. (7)   Engine Instrument Lights.  Illumination of the   engine   instruments   is   controlled   by   a   rheostat switch   placarded    ENGINE   INSTRUMENT   LIGHTS BRT  /  OFF,  located  on  the  overhead  control  panel.   The  engine  instrument  light  circuit  is  protected  by  a 5-ampere    circuit    breaker   placarded    AVIONICS,   & ENGINE  INSTR,  located  on  the  right  sidewall  circuit breaker panel. (8)   Overhead Control Panel, Subpanels, and Console  Lights.    Illumination  of  the  overhead  control panel,   subpanels,   and   console   is   controlled   by   a rheostat switch placarded OVERHEAD SUBPANEL & CONSOLE    LIGHTS    BRT    /    OFF,   located   on   the overhead   control   panel.      The   avionics   panel   and engine  instrument  light  circuit  is  protected  by  a  7-1/2 ampere circuit breaker placarded  SUB PNL OVHD & CONSOLE,    located    on    the    right    sidewall    circuit breaker panel. (9)   Side   Panel   Lights.      Illumination   of   the side    panels    is    controlled    by    a    rheostat    switch placarded  SIDE  PANEL  LIGHTS  BRT  /  OFF, located on  the  overhead  control  panel.    The  avionics  panel and  engine  instrument  light  circuit  is  protected  by  a 7-1/2-ampere circuit breaker placarded  PLT FLT SIDE PNL,   located   on   the   right   sidewall   circuit   breaker panel. b.  Cabin Lighting. (1)   No  Smoking  /  Fasten  Seat  Belt  Light.  A switch   placarded   NO   SMOKE   &   FSB   OFF  /   FSB, located   on   the   copilot's   subpanel   controls   the   NO SMOKING  /  FASTEN  SEAT  BELT sign in the cabin.   The circuit is protected by a 10-ampere circuit breaker placarded  NO  SMK  FSB  &  CABIN,  located  on  the right sidewall circuit breaker panel. (2)   Threshold  and  Aisle  Lights.    A  threshold light is installed just above floor level on the left side of the cabin, just inside the cabin door.  An aisle light is installed at floor level immediately aft of the main spar cover.  Both circuits are connected to the emergency battery  bus.    Both  lights  are  controlled  by   a  switch mounted  adjacent  to  the  threshold  light.    This  switch also  turns  the  exterior  entry  light  on  and  off.    If  the lights   are   illuminated,   closing   the   cabin   door   will automatically extinguish them. (3)   Cabin Door Latching Mechanism Light.  A light   is   provi ded   to   check   the   cabin   door   latching mechanism.      It   is   controlled   by   a   red   push-button switch    located    adjacent    to    the    round    observation window, which is just above the second step. Section XI.  FLIGHT INSTRUMENTS 2-75.  PITOT SYSTEM. a.   Pitot System R .  The pitot system, illustrated in   Figure   2-33,   provides   ram   air   pressure   for   the airspeed  indicators  and  air  data  computer.    The  pitot system  consists  of  two  pitot  masts  (one  located  on each   side   of   the   lower   portion   of   the   nose),   and associated  plumbing.    The  pitot  masts  are  protected from     ice     formation     by     internal     electric     heating elements. b.  Pitot System   T3  F3  .   The pitot and static system  provides  a  source  of  impact  air  and  static  air for  operation  of  the  flight  instruments.   A  heated  pitot mast is located on each side of the lower portion of the nose.    Tubing  from  the  left  pitot  mast  is  connected  to the  pilot’s  airspeed  indicator,  and  tubing  from  the  right pitot   mast   is   connected   to   the   copilot’s   airspeed indicator.