Auxiliary lights: white or amber front, red rear, nothing flashing

The Wisconsin Department of Transportation defines the equipment this page is about. Wis. Admin. Code § Trans 305.05(3) says an auxiliary lamp means any lamp mounted on a vehicle with a bulb having wattage in excess of 10 watts and which is not required equipment under Wis. Stat. ch. 347 or chapter Trans 305, except a spot lamp, and it lists adverse weather lamps, fog lamps, driving lamps and off-road lamps as examples. Anything under 10 watts falls outside the definition; a 55 watt driving light or an LED bar plainly does not.

Section 347.07(1) is the arithmetic. Where a vehicle with headlamps also carries adverse weather lamps, spotlamps, auxiliary lamps or any other front lamp projecting a beam of more than 300 candlepower, no more than four of them in total may be lit at once on the front of the vehicle while it is on a highway. Two headlamps plus a pair of fog lamps already reaches the limit, so switching on a light bar as well is a violation even if every individual lamp is legal.

Section 347.07(2) is the colour rule and it is unusually flat. Nothing other than white or amber may be visible from directly in front, nothing other than red may be displayed on the rear, and no flashing light of any colour may be displayed, subject only to what chapter 347 expressly authorizes elsewhere. Blue, red or green forward-facing accent lighting is therefore out on a Wisconsin car, and so is the increasingly common flashing amber grille light bought as a courtesy warning device, unless the vehicle fits one of the warning lamp categories in Wis. Stat. § 347.26. Subsection (3), the single exception written into the section itself, permits a motorcycle to carry a lighting device that illuminates the ground directly beneath it provided the device is not visible to approaching vehicles, does not display a red, blue or amber light, and does not display a flashing, oscillating or rotating light. The printed history line for § 347.07 records 2015 Wisconsin Act 27. Cars, pickups and motor homes get no equivalent underglow allowance.

Mounting and aim come from Wis. Admin. Code § Trans 305.075. Unless chapter Trans 305 or chapter 347 specifically permits otherwise, a lighted auxiliary lamp must be mounted below the level of the center of the headlamps, must direct light forward of the vehicle, must be aimed to conform with the manufacturer's recommendations so that glaring rays are not directed into the eyes of an approaching driver, and must meet the photometric specifications in SAE technical reports J581, J582 and J583. The one carve-out is practical: where added equipment such as a snow plow blocks the transmission of light from the factory installed headlights, alternate headlights may be mounted above them and used temporarily while that equipment is in place. Trans 305.075(3) then requires the operator to extinguish auxiliary lamps projecting a beam beyond the low beam headlamps when approaching an oncoming vehicle within 500 feet, or approaching or following another vehicle within 500 feet.

Off-road lamps are treated as equipment that must be physically incapable of casual use. Trans 305.075(5) allows a motor vehicle to carry auxiliary off-road lamps facing forward or rearward, but they shall be wired independently of all other lighting circuits and may not be lighted when the vehicle is operated or driven upon a highway. Wiring a roof-mounted light bar into the high-beam circuit is itself the violation, separately from ever switching it on.

Wis. Stat. § 347.26 sets out the optional lamps chapter 347 does authorize, and § 347.26(1) frames all of them alike: a vehicle need not carry them, but if it does, it may not be operated during hours of darkness unless they comply. A motor vehicle may have not more than two spotlamps, and a spotlamp may never substitute for headlamps; as an auxiliary driving light it is lawful only when set so the rays fall directly on the road surface no more than 150 feet directly in front of the vehicle and to the right of the center of the traveled roadway. Not more than two adverse weather lamps are allowed, mounted below the level of the centers of the headlamps, and they may replace headlamps only when absolutely necessary in rain, snow, dust or fog, only where two are fitted on opposite sides of the front and both are lit; with a single adverse weather lamp, both headlamps must be lit whenever it is.

The flashing warning lamps chapter 347 does permit are tied to specific vehicles and specific moments. Under Wis. Stat. § 347.26(11)(a) any vehicle may display simultaneously flashing white or amber lights to the front and amber or red to the rear, visible from 500 feet, to warn of a vehicular traffic hazard. Tow trucks must carry a flashing or rotating red lamp in addition to amber under § 347.26(6)(b), usable only while standing on or near the traveled portion of a highway preparatory to towing or servicing, and public utility, telecommunications carrier and ch. 185 cooperative vehicles may run flashing amber or, for maintenance and restoration of utility service as defined in § 347.26(9)(b), flashing green.

One more restriction catches accessory work that is not a lamp at all. Wis. Stat. § 347.10(1) provides that no headlamp, auxiliary driving lamp or auxiliary passing lamp shall have any type of decorative covering that restricts the amount of light emitted when the lamp is in use, and exempts only a covering originally equipped on the vehicle at the time of manufacture and sale.

Lighting offences in chapter 347 carry their own penalty section. Wis. Stat. § 347.30(2) provides that a person violating §§ 347.03, 347.07 to 347.12, 347.13(1) or 347.14 to 347.29 may be required to forfeit not less than $10 nor more than $200, which covers the colour rule, the four-lamp cap, the headlamp covering ban and every optional lamp in § 347.26. Violations of the administrative standards in Trans 305.075 are punished under Trans 305.04, which routes to Wis. Stat. § 110.075(7) and the same $10 to $200 range. Wis. Stat. § 347.04 makes the owner responsible for an improperly equipped vehicle, so an owner who lends the truck does not escape by not driving it.

Enforcement is roadside, because Wisconsin runs no periodic safety inspection for passenger cars. Wis. Stat. § 110.075(2) requires the operator of any motor vehicle, when directed by any traffic officer or motor vehicle inspector, to stop and submit the vehicle to inspection, and lights and turn signals are named among the items to be examined. Section 110.075(4) lets an officer order a vehicle found unsafe removed from the highway until repaired, and § 110.075(5) authorizes a repair order the owner or driver must then satisfy. Wis. Admin. Code § Trans 305.03 states the underlying duty: no person may operate or allow to be operated on Wisconsin highways any vehicle subject to the chapter that is not in conformity with it.