july2023 - 13

Experts offer tips to help solve common
and uncommon electrical and lighting
issues on commercial vehicles.
By Seth Skydel
[ WIRING ELECTRICAL ]
ighting and electrical system repairs on trucks,
tractors, and trailers are a high priority for service
operations due to their impact on safety and
uptime. The maintainers of fleets must be lightning
quick when trying to figure out why a trailer
light is out and how to fix it in order to avoid a CSA
violation. At the same time, tests and diagnostic
procedures required to speed up repairs can be
time-consuming and highly detailed.
Fortunately, technical experts and experienced
technicians across the industry have developed
best practices and tools to improve the speed and
accuracy of electrical and lighting repairs. What
follows is a series of tips that detail procedures
these subject-matter experts have found effective
to facilitate the diagnosis and repair of these
vital systems.
Identifying electrical
and electronic faults
There are three faults to look out for in electrical
and most electronic circuits, noted Terry Rivers,
senior manager of vehicle services training, Cox
Automotive Mobility Fleet Services.
These include:
High Resistance: This is the opposition to the
flow of an electric current. " If there is no current
flow, then there's no resistance, which also means
no voltage drop, " Rivers said. " Typically, you would
diagnose this high resistance fault with a voltmeter.
Today, you could diagnose this with an
infrared temperature gun or a thermal infrared
camera. " This is the most common fault.
Open Circuit: This is caused by an electrical
circuit that is not complete due to a break in the
wire, a spread terminal pin, or an interrupted
circuit. This is the second-most common fault.
Short Circuit: This is an undesirable condition
where the current travels along an unintended
path with little to no impedance. " This will lead
to the circuit being on all the time with the switch
off when there is no blown circuit protection (fuse),
or the circuit being off all the time even with the
switch on with blown circuit protection, " Rivers
said. This is the least common fault.
The first and most important step is to determine
if a circuit is power- or ground-side switched.
If it is a power-side switched circuit and the
customer complains the dome light stays on all
the time, it's impossible for this to be an issue
on the ground side. Secondly, determine inputs,
processing, and outputs. These steps can reduce
the length of wire you need to find the fault.
» First, always determine if a circuit is power- or ground-side switched.
Cox Automotive
Effectively using a
digital multimeter
Use a digital multimeter to test voltage when a
lamp or other electrical component is operating
at a reduced output, noted Dean Kennedy,
corporate training manager, Aim NationaLease.
" If the voltage available at the device in question
during operation is not equivalent to the
supply voltage, begin troubleshooting the circuit
traveling upstream toward the source, " he said.
" Once you locate the point in the circuit where
supply voltage is present, you can further isolate
the root cause.
" Using your DMM on a voltage scale, begin
comparing two points in the circuit, " Kennedy
went on. " Connect one lead to the location where
you earlier measured supply voltage and the
other lead downstream toward the device where
" A multimeter
is a better tool
because it will
tell you if you
have the right
voltage, not
just whether
or not voltage
is present. "
Dan Miller, field service
manager, Peterson
Manufacturing
1306312562 | Andrii Atanov | Getty Images
July 2023 | FleetMaintenance.com
13
http://www.FleetMaintenance.com
july2023

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