Not knowing what type of truck you have, You need some good old fashioned trouble shooting to begin. First I would check the fuses under the hood of your truck. Some have separate fuses for braking voltage vs the light voltage.
Your dealer should be able to test this and quickly determine where the problem is located.
Keep us posted!
2011 351RLTS Eagle, Mor/Ryde suspension & pin box
06 F350 Lariat PSD, SRW, LB, CC, EGR delete kit, 16K DrawTite hitch, Timbrens, TST TPMS
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