I have always wondered what the purpose is of marker lights on truck cab roofs. Is there a significance to the pattern? It always seems to be 3 lights evenly spaced in the center and 1 light on each side. I do not want them on my truck but am just curious as to the purpose of them and why the 1-3-1 pattern.

 

Norm:

I asked my father-in-law (a professional truck driver) this question. He wasn't sure of the answer, but he had a pretty good guess.

On long trips, trucks will often have a light burn out while on the road. If the lights were evenly spaced, it would be difficult to tell if the right or left light had burned out (from a distance). with the 1-3-1 pattern, the cluster of three lights determines the center of the truck. If one of the center lights burns out, no big deal (you can see the side lights and gauge the position of the truck. If a side light burns out, you can still see the center and the opposite side lights (allowing you to estimate where the burned out light is located).

I have only seen one truck with the lights evenly spaced, and that was an obvious shade tree job!

I work with a guy who used to do custom coachwork. I'll ask him. If I learn anything different I'll let you know.

 

Thanks,
That sounds like a good explanation.
Anyone else?

 

Anyone install marker lights on there roof? I was considering it. I would like to see a pic of them on a screw. Im sure it would look good though
VBSC

 

I have the roof marker lights installed on my screw and it I think it looks great. The lights cost me $150.00 to be installed. They are wired to turn on with my stock light switch. the install is very clean, it looks like a factory job.