Chevy 2500 HD Brake lights not working

The tail lights and turn signals both work as well. I have also removed the connector from the light switch module and jumped the 12V feed over to the brown wire which feeds the brake lights and they come on. The schematic in my Haynes manual indicates that there is something on the direction connector that has an impact on the stop light switch. How does the turn signal switch affect the brake circuit? Any ideas would be appreciated

I had the same symptoms. Checked fuses and bulbs to brake lights & checked good. Changed brake switch using GM parts. Problem: power steering pump fluid was low which provides/shares fluid to break booster system. Solution: topped of brake fluid because it was not even reading on the stick and bam! I had brake lights again. Not joking. It worked and read it on another thread.