Re: Correct placement of Trailer running Lights
Yellow marker lights go towards the front of the trailer, usually in front of the axle. They indicate the front of the trailer to crossing traffic. They should be on the flat side of the trailer's outer edge, not on the trailer tongue or the frame angle to the coupler. The red marker lights are on the rear of the trailer usually incorporated into the tail/stop/marker light unit. If the trailer is long enough a separate red marker light is used. There is usually only one red marker light per side, but there can be numerous yellow ones in front of it.
Marker lights are wired into the tail light sircuit. I like to add an additional yellow marker light to the front of the trailer wired into the directional signals. The 3 red light bar referred to above is needed if the trailer is over 80 " wide to indicate a wider load. Hummers have these 3 red lights due to their width, too.
hope this helps