2001 Tahoe. Brake light keeps coming on.

I have taken my wife's 2001 Tahoe LS to the Chevrolet dealership 4 times and I have yet to have it fixed. The brake light on the dashboard keeps coming on. The first two times the connector that plugs into the master cylinder was replaced. The third time the mechanic said it was a "loose" wire. The fourth time, the ABS light came on first followed shortly (same day, about 30 minutes later) by the brake light. The "wiring harness with the ABS sensor" was replaced. (The faulty connector was the one on the driver's front side.) The ABS light has not come on since then but the brake light came on the next day. The parking brake is NOT engaged. Any ideas?