New Member Problems 2003 Sierra Brake Lights

[2003Sierra Pete]

I have a 2003 GMC Sierre and I have a Brake light problem. During the
day my brake lights work fine but when I have the head lights on my
brake lights don't work. The bulb under the red lens don't work but the
light under the yellow lens comes on.

 

I changed the Electric board near the trailer hitch like my neighbor said, 40 bucks
later still have problem. Any help would be greatly appreciated.

 

Peter