I found this in the manual. It might help.
• Optional instrument cluster
Brake system warning light: To
confirm the brake system warning
light is functional, it will
momentarily illuminate when the
ignition is turned to the on position
when the engine is not running, or in a position between on and start, or
by applying the parking brake when the ignition is turned to the on
position. If the brake system warning light does not illuminate at this
time, contact your authorized dealer as soon as possible. Illumination
after releasing the parking brake indicates low brake fluid level. Contact
your authorized dealer as soon as possible.
WARNING: Driving a vehicle with the brake system warning
light on is dangerous. A significant decrease in braking
performance may occur. It will take you longer to stop the vehicle.
Contact your authorized dealer as soon as possible. Driving extended
distances with the parking brake engaged can cause brake failure and
the risk of personal injury.
http://www.motorcraftservice.com/pubs/content/~WOAEXP/~MUS~LEN/41/10expog2e.pdf
Go to page 14.