[jgattian]

The most common problem is the Brake Pedal Position Swith (BPP).

From the Ford manual;

"Brake lighting is controlled by the (REM) rear electronic module. The brake pedal position (BPP) switch is hardwired to the REM. When the brake pedal is pressed, the BPP switch will input information to the REM. The REM will process the information and output to the left, right, and high mounted stoplamps. Only the left and right stoplamps will provide lamp outage indication.

Disconnect the wire connector from the BPP switch (located on brake pedal arm). Measure the resistance between the BPP switch pin1 and pin 2 while applying the brake pedal.

Is the resistance greater than 10,000 ohms with the brake pedal released and less than 5 ohms with the brake pedal applied?

YES - Check REM operation
NO - Replace BPP switch."