Technical information

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31
Technician Guidelines for Antilock Braking Systems
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IV. ABS SPEC’ING CONSIDERATIONS
The Federal Government’s requirement for full-time
electrical power to ABSs has prompted both equipment users
and manufacturers to reconsider the way trailers are supplied
with such power. Since a particular powering configuration is
not required in the ABS rule, manufacturers and equipment
users can decide for themselves how to achieve the full-time
power requirement.
There are several different methods of supplying full time
power to the trailer ABS:
• If the auxiliary circuit of the seven-pin connector is not
in use, it can be used to supply full-time power as long
as the circuit is always “on” or “hot” when the key
switch is “on.” NOTE: Unless otherwise specified,
many manufacturers will supply a “hot” auxiliary
circuit as standard equipment. It is very important that
vehicles use this option if they are commonly coupled
to vehicles in other fleets.
• A second connector can be used specifically to power
the trailer ABS. (for example, the ISO 3731 connector)
• A special connector which is compatible with the
existing seven-pin connector can be used if it can
accommodate additional circuits (for example, a
13-pin connector).
Each of these methods has certain advantages and
drawbacks. However, it is the consensus of the members of
The Maintenance Council that the existing seven-pin connector
design should be preserved if possible for important reasons of
compatibility, safety, and maintainability.
Another important consideration is ensuring that adequate
power is available for proper ABS function. Voltage drops
between the battery and the last unit of a combination vehicle
can impact the amount of power available for the ABS,
especially in doubles and triples combinations.
For these reasons, TMC developed two recommended
practices to promote power supply and connector
standardization—TMC RP 137, “Antilock Electrical Supply From
Tractors Through the SAE J560 Seven-pin Connector,” and TMC
RP 141, “Trailer ABS Power Supply Requirements.”
To ensure adequate power is provided to the trailer from
the tractor, TMC RP 137 recommends that at least 12.5 volts be
available at the J560 connector with a 10-amp load on both the
6
2
3 5
7
4
1
Key
Pin 1: Ground Circuit
Pin 2: Clearance, Sidemarker, ID
Pin 3: Left-Hand Turn Signal
Pin 4: Stop Lamp Circuit
Pin 5: Right-hand Turn Signal
and Hazard Signal
Pin 6: Tail Lamp, Marker Lamp,
License Plate Lamp
Pin 7*: Continuous Power or
Auxiliary Circuit
(Activated in “Key On”
Position)
* Users should first consider any
prior use of Pin 7 before using this
circuit for ABSs.
Trailer Seven-Pin
Receptacle Schematic,
Using Pin 7 as a Continuous
Power Circuit for ABSs