Rear Brake Lights on 2002 Ford Expedition

This has me baffled. I am not a mechanic by no means, typical woman here, but was married to one for 12 years so I know a little about cars. On this issue I need help. I have a 2002 Ford Exp. All my rear lights work except for the brake lights. The brake light over the rear hatch works also. I changed the bulbs thinking that could be it. I got under the rear of the Exp. and made sure that the plug underneath the undercarraige was plugged in all the way and didn't come lose and also made sure it was clean. I changed the fuse. Nothing worked. I don't think it is a grounding problem because when the lights are on and I step on the brake nothing happens. The rear lights don't go out or even dim. Does anyone have any idea what it could be? I am hoping it is not an electrical problem. Any advise would be greatly appreciated.

Sharon

If you have cruise, does the cruise work? If not, check the brake switch on the brake pedal.