ATA engineering chief explains ABS powering 'convention,' pushes for single connector solution. At the recent TMC meeting in Orlando, ATA engineering vp Larry Strawhorn discussed the manufacturer and user "convention," or agreement, that relates to ABS-powering, a matter that fleets will soon have to deal with. Most tractor-to-trailer electrical systems, he notes, use the J560 electrical coupler, with coupler pin 7 known as the blue or auxiliary circuit.

On trailers built before March 1, 1998, ABS will be typically powered through pin 4 (red wire or stoplamp circuit), as required by the government. However, beginning this past March, ABS brake regulation required that all new trailers supply ABS electricity through a constant power circuit.

As of March 1, 1998, however, new trailer ABS must be designed to receive electricity through a constant power circuit and to secondarily run off the stoplight circuit when constant power is unavailable.

Through the manufacturer and user convention, the '97 and '98 constant power requirements will be met by redesignating pin 7 as the ABS constant power circuit. It will remain "hot" whenever the ignition switch is on, as has been the case for some years on certain tractors.

Providing the constant power point is not mandated by the ABS regulation. Rather, it is a procedure that has been mutually agreed upon by manufacturers and fleets to meet the ABS regulation with minimal or no change to the J560 coupler. Manufacturers will offer this convention as either optional or standard. This is the crucial change to tractor-trailer electrical systems that accommodates the ABS regulation.

It is important that fleets handling other fleets' vehicles, where exact specs may be unknown, follow the convention by providing constant power through the J560 pin 7, says Strawhorn. "Without this, some combinations may not provide constant ABS power, which could lead to liability concerns and more regulations," he emphasized.

A few fleets will be unable to follow this convention, but all must assure that they specify tractor-to-trailer systems suitable for their operations. Status determination can be made with the assistance of appropriate suppliers.

For example, certain fleets use pin 7 to power something that must be switched "off" from the cab during vehicle operation. (If pin 7 carries a signal to turn on trailer backup lamps, the convention cannot be followed without making a change.) When it's impossible to power both trailer ABS and something else through that pin, the alternatives are to change to something other than pin 7 as the constant power source, or to change the ancillary equipment's power source to something other than pin 7.

A carrier that wants to provide constant power to trailer ABS from pin 7, but is prevented from doing so because it would adversely affect another system's proper operation on the blue circuit, needs a J560 compatible connector with more pins or a second connector for the other system. (Note: Running something from pin 7 along with ABS is legal when the vehicle is stopped or moving in reverse, and also when the vehicle is moving forward, because this doesn't interfere with constant powering of ABS.)

The ABS mandate requires that on March 1, 2001, an in-cab light must signal trailer ABS malfunctions. Much like the requirement for constant power, this could destroy the standardization in tractor-trailer electrical transmission unless intervening steps are taken. One such step is a commercially available inter-vehicle electronic system that enables a malfunction signal to be sent over existing wires.

Vehicle makers may choose to use more wires and connectors to meet the 2001 requirement, warns Strawhorn, unless fleets can prove that the new signaling systems work acceptably. "Carriers must understand that if a manufacturer elects to use a second electrical cable for ABS purposes, it doubles the total number of inter-vehicle cables on a tractor/semi-trailer to 2; a set of doubles goes from 2 or 3 to 6; and a set of triples increases from 3 or 5 to 10."