Ford Repair: brake warning light stays on, brake warning light, parking brakes

Question
I just purchased a used 2003 crown victoria police car.  The parking brake warning light stays on.  Reading online there are 2 causes...low brake fluid and bad parking brake pedal position sensor.   One at a time I disconnected the connector that goes into the master cylinder and the parking brake pedal position sensor.  The parking brakes position sensor works fine.....I am at a loss as to where I should look next...BTW I am an engineer so I understand tech terms.....Thanks for your help!!   Eric

Answer
hello, give me a day or so to get back to you. i've seen this before just can't remember the repair. i want to check with one of my fellow techs
here is the pinpoint test right out of the ford manual

Test Step Result / Action to Take
 ISOLATE THE PARKING BRAKE SWITCH   
Ignition ON.
Disconnect: Parking Brake Switch C296.
Check the brake warning indicator light.
Is the light off?
Yes
If the parking brake is fully released, INSTALL a new parking brake switch.


A2 ISOLATE THE BRAKE FLUID LEVEL SWITCH   
Disconnect: Brake Fluid Level Switch C170.
Check the brake warning indicator light.
Is the light off?
Yes
If the fluid level in the master cylinder is correct, INSTALL a new brake fluid level switch.

No
GO to A3.
A3 ISOLATE THE ANTI-LOCK BRAKE SYSTEM (ABS) MODULE   
Disconnect: Anti-Lock Brake System (ABS) Module C160.
Check the brake warning indicator light.
Is the light off?
Yes
INSTALL a new ABS module. REFER to Section 206-09.

No
GO to A4.
A4 ISOLATE THE DAYTIME RUNNING LAMPS (DRL) MODULE   
Disconnect: Daytime Running Lamps Module C180.
Check the brake warning indicator light.
Is the light off?
Yes
INSTALL a new DRL module. REFER to Section 417-04.

No
GO to A5.
A5 ISOLATE THE INSTRUMENT CLUSTER/WARNING LAMPS MODULE   
Disconnect: Warning Lamps Module C2004.
Disconnect: Instrument Cluster C250.
Check the brake warning indicator light.
Is the light off?
Yes
INSTALL a new instrument cluster/warning lamps module