its cause of your single cam. j/k did u check the bulbs or change them? that happend to my barke lights and fuses and bulbs seemed fine so i decided to change em and then they worked.

 

maybe grounding out somewhere, the left rear light to mine didnt work when i bought it, and come to find out the genius who put it back in clamped the wire with a screw

 

I think i might know whats the deal, check and see if your horn works. If is dosent then its the horn fuse under the hood. Dont ask me why but when that fuse pops your brake lights are cut off as well. I drove for 6 months with no brake lights, just to find out the horn fuse was the problem.

 

Dont Sleep said it.

Ive had bulbs burn out that were still intact.

Try replacing them, you never know, just because it "looks okay" doesn't mean it is....