576 8 DIAGNOSTIC TOOLS AND ACCESSORIES
Figure 559 Checking for open circuits
Open electrical circuits can be dia
gnosed using an
ohmmeter. Disconnect the p ower su p
ply to the circuit
and isolate the circu it fro m all ot
her circuits. The circuit
between the light and the ground i
s disconnected to
prevent reading a circuit that ma
ybeshortedto
ground ahead of the load device a
s a continuous
circuit. Connect the ohmmeter
to the open ends of
the c ircuit. A high rea ding
(infinity) indicates an open
circuit. A reading near zer
o indicates a continuous
circuit. With the Flu ke 88
Digital Multim e ter (DMM),
an open circuit will read
OL (over limit).
Figure 560 Checking for short circuits
Checks for short c ircuits are similar to checks f or open
circuits. Isolate the circuit from the power source and
the ground point. Connect the ohmmeter between an
isolated circuit and a good ground point to check the
circuit for a short to ground. A short to ground will be
indicated by a reading near zero. A circuit that is not
shorted to ground will cause a high meter reading.
Measuring Duty Cycle with FLUKE 88
When measuring duty c ycle, ensure that the large dial
on the meter is p oin ting to volts DC, the DUTY button
is set to the Duty Cycle function, and the trigger has a
positive slope.
EGES-270-1
Read all safety instructions in the "Safety Information" section of this manual before doing any procedures.
Follow all warnings, cautions, and notes.
© August 2008 Navistar, Inc.
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