One problem related to brake light on has been reported for the 2003 GMC Safari. The most recently reported issues are listed below.
Backing up my boat to launch it, the brake light came on and brake pedal went to the floor. Slowed it down and ended up throwing it in park to keep the boat, trailer, and van from rolling into the water. Got towed out and a friend pulled the boat home for me. The mechanic showed me the rusted drivers side steel brake line that had ruptured. He also told me all of the other lines had considerable rust and that all of them should be replaced due to safety concerns. The entire steel brake line has been replaced and I did save the rusted lines for now.