Chevrolet TrailBlazer, Service Manual

Page: 351 / 677

The test light is used to check circuits and components while electrical current is flowing
through them. It is used for voltage and ground tests. To use a 12 volt test light, connect
the ground clip to a good ground and probe wherever necessary with the pick. The test
light will illuminate when voltage is detected. This does not necessarily mean that 12 volts
(or any particular amount of voltage) is present; it only means that some voltage is
present. It is advisable before using the test light to touch its ground clip and probe across
the battery posts or terminals to make sure the light is operating properly.
CAUTION
Do not use a test light to probe electronic ignition, spark plug or coil wires. Never use a
pick-type test light to probe wiring on computer controlled systems unless specifically
instructed to do so. Any wire insulation that is pierced by the test light probe should be
taped and sealed with silicone after testing.
Like the jumper wire, the 12 volt test light is used to isolate opens in circuits. But, whereas
the jumper wire is used to bypass the open to operate the load, the 12 volt test light is
used to locate the presence of voltage in a circuit. If the test light illuminates, there is
power up to that point in the circuit; if the test light does not illuminate, there is an open
circuit (no power). Move the test light in successive steps back toward the power source
until the light in the handle illuminates. The open is between the probe and a point which
was previously probed.
The self-powered test light is similar in design to the 12 volt test light, but contains a 1.5
volt penlight battery in the handle. It is most often used in place of a multimeter to check
for open or short circuits when power is isolated from the circuit (continuity test).
The battery in a self-powered test light does not provide much current. A weak battery may
not provide enough power to illuminate the test light even when a complete circuit is made
(especially if there is high resistance in the circuit). Always make sure that the test battery
is strong. To check the battery, briefly touch the ground clip to the probe; if the light glows
brightly, the battery is strong enough for testing.
NOTE: A self-powered test light should not be used on any computer controlled system or
component. The small amount of electricity transmitted by the test light is enough to
damage many electronic automotive components.
Multimeters
Multimeters are an extremely useful tool for troubleshooting electrical problems. A
multimeter is a voltmeter, ammeter and ohmmeter (along with other features) combined
into one instrument. It is often used when testing solid state circuits because of its high
input impedance (usually 10 megaohms or more). A brief description of the multimeter
main test functions follows:
Voltmeter-the voltmeter is used to measure voltage at any point in a circuit, or to
measure the voltage drop across any part of a circuit. Voltmeters usually have
various scales and a selector switch to allow the reading of different voltage
ranges. The voltmeter has a positive and a negative lead. To avoid damage to the
meter, always connect the negative lead to the negative (
–) side of the circuit (to
ground or nearest the ground side of the circuit) and connect the positive lead to