july2023 - 15

Intermittent turn signal failure
With an oscilloscope, noted Michael Eilbracht,
trainer, Diesel Laptops, you can look at multiple
circuits at the same time, which gives you a better
chance of finding faults faster.
" For example, let's say a bus comes in with
a complaint of left turn signals working intermittently, "
Eilbracht offered.
" In this case,
the turn signals are multiplex
controlled, meaning a
module controls how long the
turn signals are on and off.
Using three low-amp probes
with three wires in each, turn
on the left turn signals and
look at the currents coming
from the clamps. The one
channel that has the most
current is the culprit. "
Voltage drop test
procedures
In situations where the wiring
is not contained in a sealed
harness and you are able to
access both the positive and
ground circuits, you can use
a multimeter to determine
voltage drop, related Andrew
Summers, director of fleet
sales at Phillips Industries.
" First take the voltage
on the positive side wiring
from the power source to the
component to read voltage
drop, " Summers continued.
" Check the allowable drop for
the size and length of wiring
you are testing and if the
reading is outside this range,
work your way back between
connections until you find
the section of wire where the
issue is located. "
If no problems are found,
Summers said to repeat the
test on the ground side starting
at the main ground for the
component and working your
way through the ground path.
" Pay special attention to any
frame grounds, as corrosion,
paint under the connection,
and loose connections can
all create voltage drop, " he
advised. " If voltage drop is
minimal on both sides of the
circuit, then the issue is likely
the component. "
For voltage drop tests on
a sealed harness system,
Summers noted, use a multimeter
to read the voltage
at the power source for the
component. On tractors, it will
usually be at the batteries, the
alternator, or power distribuJuly
2023 | FleetMaintenance.com
15
tion panel. On trailers, unplug the 7-way cord at
the trailer, and measure the voltage at the plug on
the cable of the circuit you are testing (running
lights, clearance, brake, etc.).
If the voltage is acceptable, then plug the cable
back in.
NOTE: To determine how much voltage drop is
acceptable in a cable, use an online calculator.
Diagnostic and repair steps
" Sometimes there is more wrong than has been
reported, and it can help narrow down where the
fault is located, " said Phillip Pinter, sr. technician,
FedEx Freight. " With most circuits having multiple
lights attached, if more than one is having the
issue, it allows for points of commonality to be
looked at and get you closer to the problem. "
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july2023

Table of Contents for the Digital Edition of july2023

Hitched Up – Using AI without losing what's important to your business
Equipment – AEB adoption speeds ahead
In The Bay – Bright ideas to speed up lighting and electrical repairs
Shop Operations – Battle of the bulging budget
Lubrication – Greasing: Manual or auto?
APUS – APU innovations take heat off fleets
Diagnostics – Don't distress; de-stress your diagnostic process
Technology & Maintenance Council Annual Meeting & Skills Contest
Fleet Parts & Components
Tools & Equipment
Product Spotlight: Wheels and brakes
july2023 - 1
july2023 - 2
july2023 - 3
july2023 - 4
july2023 - 5
july2023 - Hitched Up – Using AI without losing what's important to your business
july2023 - 7
july2023 - Equipment – AEB adoption speeds ahead
july2023 - 9
july2023 - 10
july2023 - 11
july2023 - In The Bay – Bright ideas to speed up lighting and electrical repairs
july2023 - 13
july2023 - 14
july2023 - 15
july2023 - 16
july2023 - 17
july2023 - Shop Operations – Battle of the bulging budget
july2023 - 19
july2023 - 20
july2023 - 21
july2023 - Lubrication – Greasing: Manual or auto?
july2023 - 23
july2023 - APUS – APU innovations take heat off fleets
july2023 - 25
july2023 - Diagnostics – Don't distress; de-stress your diagnostic process
july2023 - 27
july2023 - Technology & Maintenance Council Annual Meeting & Skills Contest
july2023 - 29
july2023 - 30
july2023 - 31
july2023 - 32
july2023 - 33
july2023 - 34
july2023 - 35
july2023 - 36
july2023 - 37
july2023 - Fleet Parts & Components
july2023 - 39
july2023 - Tools & Equipment
july2023 - 41
july2023 - Product Spotlight: Wheels and brakes
july2023 - 43
july2023 - 44
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