Specifications

8
The Recognised Name In Security
Never use a simple incandescent (bulb) test light to probe a vehicle’s wiring.
Many modern cars today have sensitive electronics and using a “dead short” type
of probe may immediately damage, o
r set in motion to fail in the future, electronic
systems such as airbags or computers within the vehicle.
When you probe a circuit with a test light or voltmeter, the device that you are using
becomes part of that circuit and adds an additional load. Tes
t lights, on average,
have an input impedance of 100 to 200 ohms, whereas a typical voltmeter has an
input impedance of 10 million ohms. Some quick math shows that when a test light
is connected between chassis ground and a point in a vehicle circuit, it w
ill add an
additional 120mA current draw to the circuit (assuming 12 volts and the use of an
average test light). A test light with a higher input impedance will have a lower
current draw. Using the same math to calculate the current draw of a voltmeter,
i
nstallers will find that it adds only .0012 mA to the circuit.
Although logic
-
safe test lights have gained popularity in recent years, voltmeters
and multimeters have two distinct advantages. Logic
-
safe test lights do not give the
voltage reading of a cir
cuit; they only determine if it is positive or negative. And
from an economic standpoint, installers can purchase a good voltmeter for about
the same price as a logic
-
safe test light.
So, if you don’t own a good voltmeter or multimeter, go out and buy one
and learn
how to use it properly.
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