Interpretation ID: GF005930

Mr. Greg Hayes
Benson International
PO Box 970
Mineral Wells, WV 26150

Dear Mr. Hayes:

This letter is in response to your e-mail asking whether a previous interpretation letter from this agency to Mr. Larry Strawhorn is still valid. Specifically, you ask whether it is permissible to take power from the antilock brake system (ABS) power circuit of a semi-trailer in order to power other semi-trailer devices. You also ask whether it is permissible to take power directly from the ABS module.

By way of background, the National Highway Traffic Safety Administration (NHTSA) does not provide approvals of motor vehicles or motor vehicle equipment. Under 49 U.S.C. Chapter 301, manufacturers are required to certify that their vehicles and equipment meet applicable requirements. The issues raised by your letter are addressed below.

The Federal standard applicable to ABS systems in trucks and trailers with air brakes is Federal motor vehicle safety standard (FMVSS) No. 121, Air brake systems.

In a November 17, 1995, letter of interpretation addressed to Mr. Larry Strawhorn of the American Trucking Associations, the agency stated that under S5.1.6.3 of FMVSS No. 121, the ABS power circuits sole function must be to provide ABS powering, and other trailer devices may not be powered off this separate electrical circuit.

Subsequently, the agency published a final rule responding to petitions for reconsideration of the rule that required medium and heavy vehicles to be equipped with ABS (61 FR 5949, February 15, 1996). In response to the petitions, the 1996 document changed the requirements from dedicated power for trailer ABS systems to continuous power for trailer ABS systems. The relevant section of that standard now reads as follows:

S5.1.6.3  Antilock power circuit for towed vehicles.Each truck tractor manufactured on or after March 1, 1997, and each single unit vehicle manufactured on or after March 1, 1998, that is equipped to tow another air-braked vehicle shall be equipped with one or more electrical circuits that provide continuous power to the antilock system on the towed vehicle or vehicles whenever the ignition (start) switch is in the "on" ("run") position. Such a circuit shall be adequate to enable the antilock system on each towed vehicle to be fully operable. [emphasis added]

Accordingly, the February 1996 response to the petitions for reconsideration supersedes our November 17, 1995, letter of interpretation because FMVSS No. 121 no longer requires that the ABS power circuits sole function is to provide ABS powering.

To answer your specific question, S5.1.6.3 does not prohibit taking power from the ABS power circuit or the ABS module of a semi-trailer in order to power other semi-trailer devices. We note, however,that in our February 1996 response to petitions, we recognized that powering electrical devices other than the trailer ABS from the ABS power circuit has the potential to compromise the circuits ability to power the trailer ABS. We included a lengthy discussion of this issue in our notice, including a discussion of the types of devices that would not be likely to create problems. A copy of this portion of the notice (61 FR 5949 at p. 5952) is enclosed.

I hope this information is helpful. If you have any further questions about NHTSA's safety standards, please feel free to contact George Feygin of my staff at this address or by telephone at (202) 366-2992.

Sincerely,

Jacqueline Glassman
Chief Counsel

Enclosure
ref:121
d.10/21/04