TM 1-1500-204-23-1 two   leads   (in   distributor   block).      When   disconnecting ground  of  other  lead  does  not  stop  leakage,  check  for leaks between Individual leads and shielding. NOTE Rotate   crankshaft   to   a   position   that will eliminate distributor finger leakage. 9 When    a    recheck    indicates    that distributor  block  may  be  at  fault,  scrub  thoroughly  with acetone,   Federal   Specification   O-A-51,   dry   thoroughly, and  apply  a  thin  coat  of  wax  Mix  1  part  wax  to  5  parts trichloroethylene, Federal Specification O-T-634, maintained at a temperature of 130 to 140 °(54 to 60°C). 10 Repeat steps 1 through 9 above. (d) The   low-tension   system   operates   at relatively   low   voltages   (150   to   400   volts)   and   is   not seriously affected by moisture.  Check system as follows. 1 Check all accessible parts of harness and leads for chafing, broken conduit, corrosion, or   misaligned   pins   in   electrical   connectors   at   intervals specified in inspection requirements manual. CAUTION Do    not    attempt    to    repair    harness without     the     proper     special     tools. Damage    to    harness    may    otherwise result. 2 Tighten   all   loose   connectors   and tape over frayed sections of nylon covered harness 3 Test    all    low    tension    wiring    and distributor  blocks,  connection  plates,  etc,  for  continuity. Test    Insulation    resistance    with    a    tester    capable    of delivering  1000  volts  dc  (maximum)  at  1  milliampere,  or an   ohmmeter   (20,000   ohms   per   volt).      The   insulation resistance  should  exceed  1  megohm,  unless  otherwise specified (3) Spark plugs. The function of the spark plug in an ignition system is to conduct a short impulse of high voltage current through the wall of the combustion chamber.  Inside the combustion chamber it provides an air gap across which this Impulse can produce an electric spark to ignite the fuel-air charge.  For spark plug service, maintenance   Instructions,   and   list   of   approved   spark plugs, refer to TM 55-2925-200-25. (4) Ignition  switches.    All  units  in  an  aircraft ignition system are controlled by an Ignition switch in the cockpit.  The type of switch used varies with the number of engines on the aircraft and the type of magnetos used. All switches, however, turn the system off and on In much the  same  manner.    The  Ignition  switch  is  different  in  at least one respect from all other types of switches In that when the Ignition switch Is In the OFF position, a circuit is completed through the switch to ground In other electrical switches, the OFF position normally breaks or opens the circuit.  The following procedures are for Ignition  switches general maintenance. (a) Replace defective switches and broken ground wires. (b) Tighten   all   loose   switch   and   cable terminal attaching nuts. (c) For   specific   details   on   any   ignition switch, refer to applicable maintenance manual. (5) Booster  system.  Starting  aids  such  as  an induction vibrator or booster coil must be used to provide enough voltage to the spark plug.  The induction vibrator (or  starting  vibrator),  as  shown  in  figure  7-19,  consists essentially of an electrically operated vibrator, a condenser,  and  a  relay  These  units  are  mounted  on  a base  plate  and  enclosed  In  a  metal  case.    The  booster coil  assembly  as  shown  in  figure  7-20,  consists  of  two coils  wound  on  a  soft  Iron  core,  a  set  of  contact  points, and  a  condenser.    General  maintenance  of  the  booster system is described in the following procedures. (a) Repair Induction vibrators In accordance with the applicable maintenance manual and table 7-1. (b) Replace  defective  booster  coils  and all broken or frayed wiring Tighten all loose connections. (c) Replace magneto if impulse coupling is defective. 7-20