I had the same problem. 2001 Taurus SEL. Brake light would not go off, even when parking brake was released.
We did a number of things to the car before we discovered the real problem: THE ABS
First, we swapped out the brake fluid level sensor (25 bucks from Ford dealership), that did not work. Then we changed out the master cylinder and bled the brakes and that did not work.
Finally, my dear father found a couple of postings online that said that the brake light will stay on if the ABS
module fails. When my husband finally told us that the ABS
wasn't working and we noticed that the ABS
and traction control were not going through the start-up self-check, it was quite apparent what the problem was.
We sent the module to a module rebuild place in Idaho and for $160 we got a rebuild on our module. The brake light went off and the ABS
works. The self-check on all systems is working.
The dealership wanted $1300 to do this. It cost us $200 including shipping and about 4 hours of labor that we performed ourselves. And, you can drive the car without the ABS
module in place - the hydraulic brakes work just fine! So, no rental needed. Just make sure you cover the electrical connectors so they don't get wet.