TEST LIGHTS

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TEST LIGHTS

• A test light is one of the simplest testers that
  can be used to detect electricity.
• A test light is simply a light bulb with a probe
  and a ground wire attached.

FIGURE 9-1 A 12-volt test light is attached to a
good ground while probing for power.
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TEST LIGHTS
FIGURE 9-2 A test light can be used to locate an
open in a circuit. Note that the test light is
grounded at a different location than the circuit
itself.
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TEST LIGHTSContinuity Test Lights

• A continuity light is similar to a test light but
  includes a battery for self-power.
• A continuity light illuminates whenever it is
  connected to both ends of a wire that has
  continuity or is not broken.

FIGURE 9-3 Self-powered test lights contain a
battery, clamp, and probe. This type of test
light should not be used on any
computer-controlled circuits because the applied
voltage can damage delicate electronic components
or circuits.
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TEST LIGHTSLED Test Light

• An LED test light uses an LED instead of a
  standard automotive bulb for a visual indication
  of voltage.

FIGURE 9-4 High-impedance test light. An LED test
light can be easily made using low-cost
components and an old ink pen. With the 470 ohm
resistor in series with the LED, this tester only
draws 0.025 ampere (25 milliamperes) from the
circuit being tested. This low current draw helps
assure the technician that the circuit or
component being tested will not be damaged by
excessive current flow.
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TEST LIGHTSLogic Probe

• A logic probe is an electronic device that lights
  up a red (usually) LED if the probe is touched to
  battery voltage.

FIGURE 9-5 A logic probe connected to the vehicle
battery and relay used to check for power,
ground, or a pulse.
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DIGITAL MULTIMETERS

• Digital multimeter (DMM) and digital
  volt-ohmmilliammeter (DVOM) are terms commonly
  used for electronic high-impedance test meters.
• High-impedance meters, required for measuring
  computer circuits, are digital meters however,
  not all digital meters have the required 10
  megohms (M) (10 million ohms) of internal
  resistance.

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DIGITAL MULTIMETERS
FIGURE 9-6 Typical digital multimeter. The black
meter lead always is placed in the COM terminal.
Except when measuring the current in amperes, the
red meter test lead remains in the V terminal.
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DIGITAL MULTIMETERS
FIGURE 9-7 Common abbreviations used on the
display face of many digital multimeters.
(Courtesy of Fluke Corporation)
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DIGITAL MULTIMETERS
FIGURE 9-8 A summary chart indicating what
measurement type may be used to test which
vehicle system.(Courtesy of Fluke Corporation)
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DIGITAL MULTIMETERSMeasuring Voltage

• A voltmeter measures the pressure or potential of
  electricity in units of volts.

FIGURE 9-9 A typical autoranging digital
multimeter automatically selects the proper scale
to read the voltage being tested. The scale
selected is usually displayed on the meter face.
(a) Note that the display indicates 4, meaning
that this range can read up to 4 volts. (b) The
range is now set to the 40 volt scale, meaning
that the meter can read up to 40 volts on the
scale. Any reading above this level will cause
the meter to reset to a higher scale. If not set
on autoranging, the meter display would indicate
OL if a reading exceeds the limit of the scale
selected. (Courtesy of Fluke Corporation)
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DIGITAL MULTIMETERSMeasuring Voltage
FIGURE 9-10 Typical digital multimeter (DMM) set
to read DC volts.
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DIGITAL MULTIMETERSMeasuring Resistance

• An ohmmeter measures the resistance in ohms of a
  component or circuit section when no current is
  flowing through the circuit.
• An ohmmeter contains a battery (or other power
  source).
• When the leads are connected to a component,
  current flows through the test leads and the
  difference in voltage (voltage drop) between the
  leads is measured as resistance.
• Zero ohms on the scale means no resistance
  between the test leads, indicating that there is
  continuity or a continuous path for the current
  to flow in a closed circuit.
• Infinity means no connection, as in an open
  circuit.

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DIGITAL MULTIMETERSMeasuring Resistance
FIGURE 9-11 Using a digital multimeter set to
read ohms () to test this light bulb. The meter
reads the resistance of the filament.
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DIGITAL MULTIMETERSMeasuring Resistance
FIGURE 9-12 Typical digital multimeter showing OL
(over limit) on the readout with the ohms () unit
selected. This usually means that the unit being
measured is open (infinity resistance) and has no
continuity.
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DIGITAL MULTIMETERSMeasuring Resistance
FIGURE 9-13 Many digital multimeters can have the
display indicate zero to compensate for test lead
resistance. (1) Connect leads in the VO and COM
meter terminals. (2) Select the O scale. (3)
Touch the two meter leads together. (4) Push the
zero or relative button on the meter. (5) The
meter display will now indicate zero ohms of
resistance. (Courtesy of Fluke Corporation)
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DIGITAL MULTIMETERSMeasuring Amperes
FIGURE 9-14 In this digital multimeter set to
read DC amperes, note that the red lead is placed
in the far left-hand socket of the meter. The
meter is displaying the current flow (4.18 A)
through the electric fuel pump on this General
Motors 3800 V6 engine.
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DIGITAL MULTIMETERSMeasuring Amperes

• An ammeter measures the flow of current through a
  complete circuit in units of amperes.
• The ammeter has to be installed in the circuit
  (in series) so that it can measure all the
  current flow in that circuit.

FIGURE 9-15 An inductive ammeter clamp is used
with all starting and charging testers to measure
the current flow through the battery cables.
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AC/DC CLAMP-ON DIGITAL MULTIMETER

• An AC/DC clamp-on digital multimeter (DMM) is a
  useful meter for automotive diagnostic work and
  uses a Hall-effect sensor to measure current.

FIGURE 9-16 A typical mini clamp-on-type digital
multimeter. This meter is capable of measuring
alternating current (AC) and direct current (DC)
without requiring that the circuit be
disconnected to install the meter in series. The
jaws are simply placed over the wire and current
flow through the circuit is displayed.
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AC/DC CLAMP-ON DIGITAL MULTIMETER
FIGURE 9-17 An AC and DC current clamp such as
the one shown can be used with a regular digital
multimeter. The amp probe contains a separate
battery and electronic circuit that converts the
amperage reading into a millivolt (mV) signal.
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FUSE YOUR METER LEADS!
FIGURE 9-18 Note the blade-type fuse holder
soldered in series with one of the meter leads. A
10 amp fuse helps protect the internal meter fuse
(if equipped) and the meter itself from damage
that might result from excessive current flow if
accidentally used incorrectly.
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OL DOES NOT MEAN THE METER IS READING NOTHING
FIGURE 9-19 A summary of the test meter hookup.
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ELECTRICAL UNIT PREFIXES

• Electrical units are measured in numbers such as
  12-volts, 150 amperes, and 470 ohms.
• Large units over 1,000 may be expressed in kilo
  units.
• Kilo (k) means 1,000.

FIGURE 9-20 Always look at the meter display when
a measurement is being made,especially if using
an autoranging meter.(Courtesy of Fluke
Corporation)
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HOW TO READ DIGITAL METERS

• Getting to know and use a digital meter takes
  time and practice.
• The first step is to read, understand, and follow
  all safety and operational instructions that come
  with the meter.
• Use of the meter usually involves the following
  steps.
• Select the proper unit of electricity for what is
  being measured.
• Place the meter leads into the proper input
  terminals.
• Measure the component being tested.
• Interpret the reading.

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METER USAGE ON HYBRID ELECTRIC VEHICLES
FIGURE 9-24 Be sure to only use a meter that is
CAT III rated when taking electrical voltage
measurements on a hybrid vehicle.
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METER USAGE ON HYBRID ELECTRIC VEHICLES
FIGURE 9-25 Always use meter leads that are CAT
III rated on a meter that is also CAT III rated
to maintain the protection needed when working on
hybrid vehicles.