The Truck Manufacturers Assn. and the Truck Trailer Manufacturers Assn. are cautioning fleets to be aware of an unintended consequence of the FMVSS 121 amendment requiring tractors manufactured after March 1 to supply constant power for trailer antilock braking systems (ABS) when the key switch is on.

Fleets standardized on 7-way connectors should inform drivers of ABS-equipped tractors to be sure -- before hooking up to trailers -- that the constantly powered center pin is not going to unintentionally activate some piece of auxiliary equipment.

Many center pins have been wired "hot" in the past. Although these drivers should be aware of the situation, the concern is that they could experience unexpected, unintended activation of a trailer sliding undercarriage, air ride dump valve, or lift gate, leading to a hazardous situation or personal injury.

If fleets have any questions about present wiring, or need to rewire their vehicles to prevent future problems, they are urged to contact their tractor, auxiliary equipment, and/or trailer manufacturer.