TM  10-3930-643-34 GENERAL  MAINTENANCE  PROCEDURES.  (cont) 2-13. Electrical  Repair. Specific  electrical  system  maintenance  tasks  are covered in Chapter 5 of this manual. The following are general electrical repair a. b. c. due to d. e. practices  and  procedures: Clean electrical ground contacts with crocus cloth or emery cloth. Make sure that all connections are tight. Electrical wires,   cables  and  connections  should  be  checked  for cracks aging and for exposed wires which could cause an electrical short. Use distilled water for batteries. If unavailable, use clean water. Use of multimeter. Maintenance functions authorized for performance at the organizational level require the use of the multimeter. Wire,  harness  and cable repairs may be indicated as a result of tests performed with the multimeter. Procedures  for  repairing  these  electrical  components  can  be  found in Chaper 5. After any repairs or replacements are done, test again. The following  procedures  outline  the  uses  of  the  multimeter  for  electrical  testing: (1) Using the ohms scale. The ohms scale is used to make tests for continuity,  shorts  and  resistance. NOTE Proper  operation  of  electrical  components  depends  upon  proper  ground- ing. In all troubleshooting procedures of devices which depend on screws or physical contact for their electrical ground (lamp sockets, transmitters, batteries, etc.) use a jumper wire from the device to the hull to check grounding. The multimeter must be set up and zeroed before making these tests. Perform the following steps for the multimeter you are using: (a)  AN/URM-105. 1 Set selector switch (1) to Xl ohms position. 2 Now zero the meter. Touch the two probes (2) together while turning OHMS ADJ knob (3) until needle (4) is over 0 on the top scale. 3 If needle will not zero, replace the batteries. If needle still will not zero after replacing the batteries, turn in the multimeter for repair. 2-10