TM-9-2350-311-20-1
HOWITZER, MEDIUM, SELF-PROPELLED, 155MM; M109A2, M109A3, M109A4 AND M109A5
TECHNICAL MANUAL; UNIT MAINTENANCE MANUAL FOR HULL, POWERPLANT, DRIVE CONTROLS, TRACKS, SUSPENSION, AND ASSOCIATED COMPONENTS
AUGUST 1994
TM-9-2350-311-20-1 - Page 57 of 1275
TM 9-2350-311-20-1
2-12.3 Using the Ohms Scale
The ohms (
) scale is used to test for continuity, shorts, and resistance.
Proper operation of electrical components depends upon proper grounding. In all troubleshooting procedures of
components that 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.
2-12.4 Testing for Short Circuits
A short circuit occurs when two circuits (electrical Ieads/wires) that should not be connected make contact with each
other. A short also occurs when a circuit that should not touch ground makes contact with ground. To check for shorts,
do the following steps:
a. Set up multimeter.
CAUTIO N
Failure to do the following steps can damage the multimeter.
b. Disconnect circuit being tested from power source. To be safe, disconnect battery ground strap.
c. Connect one probe to one circuit and other probe to other circuit or ground (if checking for a short to ground).
The example shows a check to see if wire A is shorted to wire B in wiring harness.
d. Observe multimeter reading.
Ž If multimeter indicates zero (0)
impedance, circuits are shorted.
• If multimeter indicates infinite
impedance, circuits are not shorted.
• If multimeter reading jumps or changes, circuits are intermittently short circuited.
2-9
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