Hey, wired up71, need more info!
Like djKale said, what year? I assume it's a Seville. Why do you think it has something to do with the brake lights? Are they staying on? Were there any other symptoms? Is there anything else not working? Fuses usually cover more than one item.
The cruise control on older models (about '92-97) are pretty much self-contained, so if the cruise switch and brake light switch are eliminated as the problem, the stepper motor module is usually the culprit. They're expensive, so check with your local salvage yard or borrow one from a good friend for testing. They are interchangable from model to model. I've used one off a Chevy PU on a Buick before. Just changed the mount. I think the '98(?) and up are GM wide also. The pre '92 models are vacuum operated and have a control module under the dash.
I might be off on the years. I'm somebody can help with that.
Good luck and let us know what you find.