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 DRAFT
TB 9-2320-279-13-1
FIELD LEVEL TROUBLESHOOTING INTRODUCTION - Continued
(c) If the resistance being measured is connected to a circuit, turn ENGINE switch OFF.
(d) Connect 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.
(e) Read the resistance value on the digital display.
2. Continuity checks.
(a) Place the function/range switch in any ohm range.
NOTE
Some meters show "l+m", or simply "l" when functioning/range switch is in any ohm
position.
(b) Connect the red test lead to the volt-ohm connector and black lead to COM input connector on the
meter. When the test leads are separated or measuring an out-of-range resistance, the digital
display will indicate "OL" (Over Limit).
(c) Put one test probe at one end of the wire or circuit to be tested. Use the other test lead to trace the
circuit. When continuity is established, an ohm symbol will appear in the upper left corner of the
digital display. If contact in the wire is maintained long enough (about 1/4 of a second), the OL
display will disappear and the resistance value of the wire or circuit will appear next to the symbol.
A resistance value of 200 ohms or less indicates continuity is being measured.
(d) If your multimeter does not work in this manner, learn how it operates before performing
troubleshooting.
3. Voltage measurements. The HEMTT truck is equipped with 24 vdc circuits. Troubleshooting
procedures will reference 24 vdc measurements, however these values can vary. When the batteries
are fully charged, 25.2 vdc can be measured on an open 24 volt circuit and 29 vdc can be measured
when the engine is running at 1000 rpm.
(a) Connect the red test lead to the volt-ohm input connector and the black lead to the COM input on the
meter. If a DC-AC switch is present, make sure it is set to the DC position.
(b) Set the function/range switch to the desired volts position. If the magnitude of the voltage is not
known, set the switch to a range which will be able to read most voltages seen on the truck
(typically, a 200V range will do). Then reduce the range until a satisfactory reading is obtained.
(c) Connect the test leads to the circuit being measured. Following the voltage measurement point, the
color test lead tube used is given in parenthesis (red is volt-ohm connection and black is the COM
connection).
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