i have no break lights on the truck other than the break light on the cab of the truck.. In the rear of the truck i have marker lights, turns signals, and reverse but the break light wont light up when you step on the brakes..

 

Have you checked Fuses?

 

as suggested, first check all the fuses. if they are all good, than i would look at the multifunction switch.

 

It is really likely to be the multifunction switch if the center brake light works and the turn signals work.

 

I've heard of guys just cleaning the multi function switch and that doing the trick. They can get pretty funky

 

Check your trailer wiring too.