TM 9-2320-363-20-1
Section 2
BASIC KNOWLEDGE REQUIRED
Before using this manual, there are some areas that you should be familiar with. With this basic knowledge, you will have
success using the diagnostic charts.
A.
ELECTRICAL CIRCUITS
You should understand the theory of electricity and know the meaning of voltage and ohms. You should
understand what happens in a circuit with an open or shorted wire. You should be able to read and understand a
wiring diagram.
You should be able to use jumper wires to make circuit checks.
B.
USE OF DIGITAL VOLT-OHM METER
You should be familiar with the digital volt-ohm meter. You should be able to measure voltage and resistance. You
should be familiar with the controls of the meter and how to use it correctly. Instructions for use of a typical digital
volt-ohm meter are as follows:
Resistance Measurements
1.
Connect the red test lead to the V-Q (Volt-Ohm) input connector and the black lead to the com input
connector on the
meter.
2.
Set the function/range switch to the desired Q position. If the magnitude of the resistance is not known, set
the switch to the highest range, then reduce until a satisfactory reading is obtained.
3.
If the resistance being measured is connected to a circuit, turn off the power to the circuit being tested (turn
off ignition).
4.
Connect the test leads to the circuit being measured. When measuring high resistance, be careful not to
contact adjacent points, even if they are insulated. Some insulators have a relatively low insulation
resistance which can affect the resulting measurement.
5.
Read the resistance value on the digital display.
Continuity Checks
In addition to measuring the specific resistance value of a circuit, some meters will also tell if a continuous electrical
path exists. If a path exists, the circuit is said to have "continuity." (This continuity check can be used in any section
of the DDEC III Troubleshooting Guide where the test is looking for greater than, less than, or equal to 5 ohms.) An
open circuit (broken electrical path) would have co resistance and would not have continuity. To utilize this
continuity feature of certain meters:
1.
Place the function/range switch in any Q range.
2.
Connect the red lead to the V-Q connector and the black lead to the com connector on the meter. With the
test leads separated or measuring an out-of-range resistance, the digital display will indicate "OL" (overlimit;
some meters show "1 +", "", or simply "1").
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