My rear brake lights are not working.

[edlmann]

This may sound like a dumb question, but did you try replacing the bulbs?

Edit: Wait, sorry, didn't see you said your turn signals worked. Do you have trailer wiring on your truck?

The brake lights and turn signals use different parts of a dual element bulb, so your first comment was plausible. The fact that both went out at the same time made me skeptical about a bulb problem.