FORD 2006 Mustang v.2 - Manual (Page 152)

Do not drive your vehicle until you verify that the brakelamps
are working.
Always set the parking brake fully and make sure the gearshift is
latched in P (Park). Turn the ignition to the LOCK position and
remove the key whenever you leave your vehicle.
If the parking brake is fully released, but the brake warning lamp
remains illuminated, the brakes may not be working properly.
See your authorized dealer.
2006 05+ Mustang (197)
Owners Guide (post-2002-fmt)
USA (fus)
Driving
152