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12 Volt Test Light
The 12 volt test light is used to check circuits and components while electrical
current is flowing through them. It is used for voltage and ground tests. Twelve
volt test lights come in different styles but all have three main parts; a ground
clip, a probe, and a light. The most commonly used 12 volt test lights have pick-
type probes. To use a 12 volt test light, connect the ground clip to a good ground
and probe wherever necessary with the pick. The pick should be sharp so that it
can penetrate wire insulation to make contact with the wire, without making a
large hole in the insulation. The wrap-around light is handy in hard to reach areas
or where it is difficult to support a wire to push a probe pick into it. To use the
wrap around light, hook the wire to be probed with the hook and pull the trigger.
A small pick will be forced through the wire insulation into the wire core.
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
glows, you know that there is power up to that point; if the 12 volt test light does
not glow when its probe is inserted into the wire or connector, you know that
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 does glow. When it does
glow, the open is between the probe and point previously probed.
The test light does not detect that 12 volts (or any particular amount
ofvoltage) is present; it only detects that some voltage is present. It
isadvisable before using the test light to touch its terminals across the
batteryposts to make sure the light is operating properly.
Self-Powered Test Light
The self-powered test light usually contains a 1.5 volt penlight battery. One type
of self-powered test light is similar in design to the 12 volt test light. This type
has both the battery and the light in the handle and pick-type probe tip. The
second type has the light toward the open tip, so that the light illuminates the
contact point. The self-powered test light is a dual purpose piece of test
equipment. It can be used to test for either open or short circuits when power is
isolated from the circuit (continuity test). A powered test light should NOT be
used on any computer controlled system or component unless specifically
instructed to do so. Many engine sensors can be destroyed by even this small
amount of voltage applied directly to the terminals.
may overheatand possibly melt. Never use jumpers to bypass high
resistance loads (such asmotors) in a circuit. Bypassing resistances, in
effect, creates a short circuitwhich may, in turn, cause damage and
fire. Never use a jumper for anythingother than temporary bypassing
of components in a circuit.
WARNING
Do NOT use a test light to probe electronic ignition spark plug or
coilwires. Never use a pick-type test light to probe wiring on computer
controlledsystems unless specifically instructed to do so. Any wire
insulation that ispierced by the test light probe should be taped and
sealed with silicone aftertesting.
Стр . 4 из 16 UNDERSTANDING AND TROUBLESHOOTING ELECTRICAL SYSTEMS
18.11.2005 http://www.chiltondiy.com/content/8687/8687_6_1.html