TM 1-1500-204-23-4 NOTE · Remove components from aircraft when replacing brushes. · If    brushes    are    worn    to    or beyond allowable limits, brush leads are deteriorated, commutator   shows   evidence of excessive arcing, or if metal particles  are  present,  replace the starter. Figure 3-11.  Microswitch e.  Switches.  Switches control the current flow in most aircraft electrical circuits.  A switch is used to start, stop, or change direction of current flow. (1)  Types.    Toggle  (see  figure  3-10),  push- button, micro switches (see figure 3-11), rotary-selector (see  figure  3-12),  and  relay  switches  are  used  in  Army aircraft.  Toggle switches are used more than any other type of switch. (2) Inspection. General inspection procedures for switches are as follows: (a)   Inspect   terminals   for   distortion, malformed threads, and corrosion. (b)   Operate   switch   and   observe   for proper actuation. (c)     Inspect     switch     and     mounting hardware for malformed threads and damage. (3) Replacement criteria.  Replace switches when moving parts are binding, scraping, or have dead spots    as    evidenced    by    erratic    operation    of    their respective  components.    Replace  switches  that  do  not pass a continuity check. NOTE Replace    toggle    switches    when dust boots are deteriorated. f.  Built-In Test Equipment.  Built-in test equipment is used to test various systems while installed upon the aircraft.      When   button   or   switch   is   activated   a   light comes    on    to    indicate    system    continuity    or    proper operation.  Built-in test equipment is commonly used in communication    systems,    fire    warning    systems,    and weapon systems. g.    Electronic  Control  Units.    Electronic   control units     provide     regulated     power     and     contains     the necessary  information  to  control  weapon  systems  and other electronic equipment on Army aircraft. (1)   Types.      Various    types    are    used    to regulate   APU,   weapon   systems,   and   other   installed equipment. (2) Inspection. General inspection procedures for electronic control units are as follows: (a) Inspect case for cracks or dents. (b) Inspect for secure mounting. (c)   Inspect   electrical   connectors   for broken pins, cracked inserts, or corrosion in accordance with TM 1-1500-343-23. (3) Replacement criteria.  Electronic control units  shall  be  replaced  if  case  is  damaged  or  unit  is found   to   be   defective.      Perform   functional   check   in accordance     with     the     applicable     technical     manual. Change 3  3-17