How Can A Stop Light Also Function While "running"?

My school has running (meaning when the front lights are on, running lights are on) as function of the stop lights on the tractor and trailer. How is that possible? If they are on you can not use them to indicate when the truck is stopping.

Okay I am confused, are all the lights working properly? If you're electrical connector is plugged in and working properly, when you press on the break peddle your tail break lights should light up. If they don't , the problem could be a break light is out or there is some other malfunction. Hopefully Kearsey whom seems to be one of the most knowledgeable people here and no doubt has PhD in electrical engineering will be able to to answer your question better than me

I think User B is wondering how "stop lights" can be "running lights" at the same time. Often a light box on the back of either the tractor or trailer has the dual function of Tail Light that indicates the back end of a vehicle and Stop Light that only comes on when the brakes are applied.

Running Lights simply highlight at least the corners of the unit. Note that running lights are amber except for the back end where they are red.

Your "running lights" that also function as "stop lights" have two different levels of brightness. When the brake is applied they light up considerably brighter than they are while being used as running lights. They have a dual function.

Dual filament bulbs,, simple..clearance,marker, lots of other bulbs are single filament....

Check em out next time you're in an auto parts store......Besides what does it even matter ??? LOL