Here is the WA State RCW on Required Lighting;
RCW 46.37.090
Additional equipment required on certain vehicles.
In addition to other equipment required in RCW 46.37.040, 46.37.050, 46.37.060, and 46.37.070, the following vehicles shall be equipped as herein stated under the conditions stated in RCW 46.37.080, and in addition, the reflectors elsewhere enumerated for such vehicles shall conform to the requirements of RCW 46.37.120(1).
(1) Buses, trucks, motor homes, and motor vehicles with mounted campers eighty inches or more in over-all width:
(a) On the front, two clearance lamps, one at each side, and on vehicles manufactured or assembled after January 1, 1964, three identification lamps meeting the specifications of subdivision (6) [(7)] of this section;
(
On the rear, two clearance lamps, one at each side, and after January 1, 1964, three identification lamps meeting the specifications of subdivision (6) [(7)] of this section;
(c) On each side, two side marker lamps, one at or near the front and one at or near the rear;
(d) On each side, two reflectors, one at or near the front and one at or near the rear.
(2) Trailers and semitrailers eighty inches or more in over-all width:
(a) On the front, two clearance lamps, one at each side;
(
On the rear, two clearance lamps, one at each side, and after January 1, 1964, three identification lamps meeting the specifications of subdivision (6) [(7)] of this section;
(c) On each side, two side marker lamps, one at or near the front and one at or near the rear;
(d) On each side, two reflectors, one at or near the front and one at or near the rear: PROVIDED, That a mobile home as defined by RCW 46.04.302 need not be equipped with two side marker lamps or two side reflectors as required by subsection (2) (c) and (d) of this section while operated under the terms of a special permit authorized by RCW 46.44.090.
(3) Truck tractors:
On the front, two cab clearance lamps, one at each side, and on vehicles manufactured or assembled after January 1, 1964, three identification lamps meeting the specifications of subdivision (6) [(7)] of this section.
(4) Trailers, semitrailers, and pole trailers thirty feet or more in over-all length:
On each side, one amber side marker lamp and one amber reflector, centrally located with respect to the length of the vehicle: PROVIDED, That a mobile home as defined by RCW 46.04.302 need not be equipped with such side marker lamp or reflector while operated under the terms of a special permit authorized by RCW 46.44.090.
(5) Pole trailers:
(a) On each side, one amber side marker lamp at or near the front of the load;
(
One amber reflector at or near the front of the load;
(c) On the rearmost support for the load, one combination marker lamp showing amber to the front and red to the rear and side, mounted to indicate maximum width of the pole trailer.
(6) Boat trailers eighty inches or more in overall width:
(a) One on each side, at or near the midpoint, one clearance lamp performing the function of both a front and rear clearance lamp;
(
On the rear, after June 1, 1978, three identification lamps meeting the specifications of subsection (7) of this section;
(c) One on each side, two side marker lamps, one at or near the front and one at or near the rear;
(d) On each side, two reflectors, one at or near the front and one at or near the rear.
(7) Whenever required or permitted by this chapter, identification lamps shall be grouped in a horizontal row, with lamp centers spaced not less than six nor more than twelve inches apart, and mounted on the permanent structure of the vehicle as close as practicable to the vertical centerline: PROVIDED, HOWEVER, That where the cab of a vehicle is not more than forty-two inches wide at the front roof line, a single identification lamp at the center of the cab shall be deemed to comply with the requirements for front identification lamps.
