TM 10-3930-659-20 2-20. HEAT SHRINKABLE TUBING. Use  heat  shrinkable  tubing  (Item  39,  Appendix  C)  to  insulate  soldered  and  crimped  electrical  connections  as follows: (1) Cut desired length of new heat shrinkable tubing twice the diameter of the connection to be covered. (2) Slide the heat shrinkable tubing onto the wire and out of the way before making electrical connection. (3) After making electrical connection, slide heat shrinkable tubing into place over electrical connection. WARNING DO  NOT  touch  heat  shrinkable  tubing  for  at  least  30  seconds  after  heating.    Heat shrinkable tubing Is hot and will burn you. (4) Hold  heat  gun  (Item  19,  Appendix  F)  4-5  in.    (10.2-12.7  cm)  away  from  heat  shrinkable  tubing  and apply heat for approximately 30 seconds.  Stop applying heat as soon as heat shrinkable tubing forms to the shape of the electrical connection. 2-21. ELECTRICAL GROUND POINTS. Many electrical problems are the result of poor ground connections.  You can ensure that ground connections are good by performing the following steps: WARNING Although battery disconnect switch must be on and battery ground cable connected in order to test electrical circuit voltage, turn off battery disconnect switch or disconnect battery  ground  cable  before  performing  resistance  tests  or  replacing  parts.    This  will prevent shock to personnel, and damage to parts and equipment. (1) Remove hardware connecting ground cable terminal lug to ground point. WARNING Dry cleaning solvent, P-D-680, is toxic and flammable.  Always wear protective goggles and gloves, and use only In a well-ventilated area.  Avoid contact with skin, eyes, and clothes, and DO NOT breathe vapors.  DO NOT use near open flame or excessive heat. The solvent's flash point Is 100°F-138°F (380C-59°C).  If you become dizzy while using cleaning solvent, immediately get fresh air and medical help. If solvent contacts eyes, Immediately wash your eyes and get medical aid. (2) Clean mounting hardware, ground cable terminal lugs, and ground point with dry cleaning solvent (Item 31, Appendix C) and scrub brush (Item 5, Appendix C). (3) Remove any rust with wire brush (Item 6, Appendix C) and crocus cloth (Item 8, Appendix C). 2-11