Kia 2005 Break Lights

I have a Kia Sorento 2005! The break lights are not working. They are bright and do not dim when I take my food off the break. I have replaced the fuse, the bulbs, and the switch located above the break peddle. The break lights work if the head lights are off, but the second you turn the headlights or fog lights on the break lights don't work. What is my next move?

Thank you for any help you can provide.

Court