97 Chevy Van Brake Lights Problem

Hava 97 Chevy Van which with the heads light off it has brake lights, but when the head lights are on it does not. Any ideas? Somewhere there is probably a ground wire with corrosion or a loose connection. Sorry I can't offer any more help. Maybe a GM guy will show. What type of van? Venture, astro?

Waht modle 3500 or a G van.

Your not giving me much to work with.

How about year,make modle and engine size. It is a 2001 2500 Express van with a V8, Took the rear light asm apart and checked all the grounds and connections could see anything bad or any grounds that were loose or corroded in that area.