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Operator’s Manual Vehicle Maintenance CXU,
CHU, GU, TD, MRU and LEU 47
Precautions When Installing Electrical Equipment
Connecting electrically powered or electrically controlled equipment to a vehicle
may cause interference with other vehicle electrical or electronic equipment (such as
ABS systems, Rollover Stability Systems, etc.). The amount of interference depends
upon the operating frequency of any new signals and the degree to which transient
signals are coupled to the vehicle system.
Note: Whenever new electrical equipment is installed, it is the obligation of the
installer to ensure that the new equipment does not interfere with the proper operation
of all other electrical systems on the vehicle.
If new electrical equipment is installed, a vehicle checkout procedure should be
performed.
1 Perform the checkout procedure under the following conditions:
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Engine running
Brake system air pressure in operating range
Vehicle stationary
Brake pedal fully depressed
2 Operate the new equipment under all starting, running and sutdown conditions.
3 Listen for signs of air exhausting from the ABS modulator valves (which is an
indication of an interference condition).
4 Correct all interference conditions before operating the vehicle.
Note: The center pin of the standard seven-pin trailer electrical connector has been
standardized as the dedicated connection for uninterrupted power for trailer ABS. This
pin is always hot when the tractor ignition is turned on.
DANGER
Some trailers manufactured prior to
the trailer ABS regulations may use
the center pin to power certain trailer
auxiliary equipment. The possibility
exists that this auxiliary equipment may
be unexpectedly activated by the truck
or tractor electrical system, resulting in
personal injury or damage to equipment.
Caution must be used when connecting
the trailer electrical connector to ensure
that power to the center pin will not
unintentionally activate any trailer
auxiliary equipment.