5-8. INTRODUCTION TO LOGIC TREE TROUBLESHOOTING (CONT).
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 relative low insulation
resistance which can affect the resulting measurement.
Read the resistance value on the digital display.
Place the function/range switch in any ohm range.
Some meters show "1+m", or simply "1" when function/range switch is in any ohm position.
Connect the red lead to the volt-ohm connector and black lead to COM input connector on the
meter. With the test leads separated or measuring and out-of-range resistance, the digital display
will indicate "OL" (Over-Limit).
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 will
disappear and the resistance value of the wire or circuit will appear next to the symbol.
If your multimeter does not work in this manner, read the manufacturer's operating instructions
before performing troubleshooting.
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 switched to the DC position.
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 trailer. Then
reduce the range until a satisfactory reading is obtained.
Connect the test leads to the circuit being measured. Following the voltage measurement point, the
color test tube used is given in parenthesis (red is volt-ohm connection and black is the COM
5-9. DIRECT SUPPORT (DS) TROUBLESHOOTING PROCEDURES.
Refer to Table 5-1 for a list of common malfunctions which are found in the troubleshooting procedures. The
troubleshooting procedures contain test and inspection instructions required to determine the malfunction's cause and
corrective actions for repairing the faulty equipment. Before troubleshooting, be sure all Preventive Maintenance
Checks and Services (PMCS) have been performed. Try to return the component to operation after each test,
inspection and corrective action has been performed.