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Wire Harness Test Simple


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a very basic presentation for simple testing

a very basic presentation for simple testing

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  • 1. 1
    Testing a Wire Harness
    Ronald Spohrer
  • 2. 2
    Two methods of testing a harness using a Multimeter
    • The Ohmmeter
    • 3. The Voltmeter
  • 3
    Safety Reminder
    Before testing any circuit, remember personal safety and equipment
    Wear Glasses, hearing , and gloves
    Working with electricity, it is possible for:
  • 4. 4
    Testing with an Ohmmeter
    Test meter to make sure it is working
    Isolate the component or segment of the circuit that is to be tested
    Set the meter on the Ohm Scale.
    Hint: Look for the upside-down horse shoe
  • 5. 5
    Remove the current (power/voltage)
    At the source by removing the fuse
    Turning off the ignition switch, that is if the circuit is controlled by the switch
    Disconnect from the power source, battery
  • 6. 6
    Connect the probes or leads
    One at the start or beginning of the circuit and the other at the end
    If there is continuity (no break) the meter will show zero or low resistance.
    That is 000 or possibly a few ohms of resistance depending on the length of wire, connections, and number of devices in line.
  • 7. 7
    If there is a break or open wire the meter will read 1. or UL
    If there is a break:
    Keep moving from the end back to the source to isolate the break
    Check each connection that is in line on that circuit
  • 8. 8
  • 9. 9
    Testing with a Voltmeter
    Test the meter make sure it is working
    Set the meter to the DCV scale matching the circuits voltage and the vehicles
    This could be 6v, 12v, 24v, 36v, 48v, 120v.
  • 10. 10
    Attach the negative probe, the black lead, to the ground of the vehicle
    Using the positive probe, the RED lead,
    Start at the source of the circuit
    Check for voltage working from the beginning to the end of the of the circuit
  • 11. 11
    Example:start at the beginning and progress to the end of the circuit
    Master switch
    Ignition switch
    The end may be a light
  • 12. 12
    Voltmeter Safety Cautions
    Leave the ground lead (negative lead) connected at all times to a good clean spot
    When the circuit is energized, it may move a function of the machine
    Always a possible shock hazard
  • 13. 13
    If voltage (power, current) is to and through the light or end use device, but still not working, then most likely the problem is in the ground side of the circuit.
    If possible, check the ground connections
    Are they clean, tight, and in good state of repair?
    Replace the connection or wire as needed
  • 14. 14
  • 15. 15
    Testing the Wiring Harness
    The wiring harness is the main branch with which electrical needs of a machine and its components are met
    Wires are commonly sheathed to protect
    Wires emerge at points along the frame for usage as needed by the machine
  • 16. 16
    Wire Harness
    If a bad wire is found:
    Individual wires can be repaired or replaced as needed
    Replace a wire by cutting off the ends of the defective wire and discard
    Run a new wire along and attach with plastic clips and electrical tape
  • 17. 17
    Wire Harness
    Always use the same size wire.
    A smaller wire will not carry the load and in turn will overheat or melt.
    Do not attempt to thread a new wire into the harness as this may damage other wires in the harness.
  • 18. 18
    Wire Harness
    Electricity needs a complete circuit to follow
    It will take the path of least resistance
    When testing a harness one needs to move the harness around when testing with your meter connected
  • 19. 19
    Wire harness
    Test for open wire (broken wire)
    A-D } infinite resistance
    A-C } infinite resistance
    A-B } infinite resistance
  • 20. 20
    Wire Harness
    Tests for short
    Bare wire touching frame
    A-D} zero
    A-C} infinite
    A-B} zero if wire intact but grounded
    A-B} infinite if wire is broken but not touching ground
  • 21. 21
    Wire Harness
    Testing for short, two wires touching
    A-C} zero
    A-B} zero
    A-D} zero if wires touching frame
    A-D} infinite if wires are not touching frame
  • 22. 22
  • 23. 23
    Blown Fuses
    Not always a short
    Possible temporary overload
    (ice in fan, too many added on devices)
    Incorrect fuse size
    Poor contacts - pitted, corroded, excessive resistance
  • 24. 24
    Need to stress check grounds
    Clean, tight, free of corrosion
    One major reason, more and more plastic being used
    Probe at the connection not the wire, every extra hole in wire a place for future problems
    Personal safety and equipment
  • 25. 25
    In review
    Two methods of testing a harness using a Multimeter
    The Ohmmeter
    The Voltmeter