Ms. Lynn Schultz
SB Solutions LLC
1907 Brooks Ct.
West Bend, WI 53090-1789
Dear Ms. Schultz:
This responds to your letter regarding the disconnection of the front lights on trucks, when using an auxiliary attachment, under Federal Motor Vehicle Safety Standard (FMVSS) No. 108, Lamps, Reflective Devices, and Associated Equipment. Specifically, you asked whether it would be permissible for a motor vehicle repair business to modify a vehicle with a special plow that includes a set of auxiliary front vehicle lamps. When attached, this plow would disconnect the high and low beam headlights, the turn signals, and the front marker lamps on the truck. As discussed below, it would be acceptable to disconnect these lamps on trucks if the auxiliary lamps on the snow plow met all of the requirements of FMVSS No. 108 for the disconnected lamps.
By way of background, the National Highway Traffic Safety Administration (NHTSA) is authorized to issue FMVSSs that set performance requirements for new motor vehicles and items of motor vehicle equipment (see 49 U.S.C. Chapter 301). NHTSA does not provide approvals of motor vehicles or motor vehicle equipment. Instead, manufacturers are required to self-certify that their products conform to all applicable safety standards that are in effect on the date of manufacture. NHTSA selects a sampling of new vehicles and equipment each year to determine their compliance with applicable FMVSSs. If our testing or examination reveals an apparent noncompliance, we may require the manufacturer to remedy the noncompliance, and may initiate an enforcement proceeding if necessary to ensure that the manufacturer takes appropriate action.
A relevant provision of Federal law with respect to equipping a vehicle with a snow plow is 49 U.S.C. 30122(b), which specifies that:
A manufacturer, distributor, dealer, or motor vehicle repair business may not knowingly make inoperative any part of a device or element of design installed on or in a motor vehicle or motor vehicle equipment in compliance with an applicable motor vehicle safety standard prescribed under this chapter unless the manufacturer, distributor, dealer, or repair business reasonably believes the vehicle or equipment will not be used (except for testing or a similar purpose during maintenance or repair) when the device or element is inoperative.
Ordinarily, if a motor vehicle repair business disconnected the front lights on trucks, it would be a violation of 30122. However, assuming the plow contains a set of auxiliary lamps that meets all of the requirements of FMVSS No. 108 for the lamps being replaced, it would be permissible to disconnect the lamps in this instance.
As you have not fully described the characteristics of the auxiliary lamps, or the precise nature of the trucks you plan to install this snow plow on, we cannot say whether your specific design would comply with FMVSS No. 108. We note, however, that you state that the auxiliary lights would have the Hi and Lo beam headlamps, turn [signal] lamps, and marker lamps. Standard No. 108 requires headlamps, turn signals, and parking lamps on the front of the vehicle. If the vehicle is over 80 inches wide, clearance and identification lamps are also required on the front of the vehicle. All of these lamps must conform, when installed, to the performance and location requirements set forth in FMVSS No. 108.
Finally, we are enclosing a 1999 letter of interpretation issued by NHTSA to a different manufacturer of auxiliary lamps for use with vehicles on snow plows. This letter explains in some detail the responsibilities and potential liabilities of manufacturers and installers with regard to the installation of these lighting devices, and it is our hope that it assists you with any further questions you may have.
If you have any further questions, please contact Ari Scott of my staff at (202) 366-2992.
Anthony M. Cooke
 While you have referred to these lamps as auxiliary, generally NHTSA uses that term to describe supplemental lamps not required by FMVSS No. 108. In the situation you describe, these auxiliary lamps would be serving as lamps required by the standard.
 January 22, 1999 letter to Mr. Fred Kelly, available at http://isearch.nhtsa.gov.