Possible ground issue at the taillights.
Check the switch on the brake pedal
if you recenly replaced bulbs u may have installed them backwards they should be running lights and brake lights if this is the case they maybe installed incorrectly
brake light switch would be most common cause
Bad ground on the brake lite circuit.
A bad ground wire will cause dim headlights, or will cause lights not to work.
i found it to be the tail light harnesses go bad . a common problem with them because the bulb sockets short out.
It may be wired wrong.
BAD BRAKE LIGHT SWITCH AT TOP OF BRAKE PEDAL
It sounds like a blown fuse or a bad head light switch
I would check the rear bulbs. I just had this issue and it ended up my brother had used the wrong bulb, and odd enough it caused the brake lights to stay on with headlights. When headlights were not on and you applied the brakes the dash would light and brake lights worked. Strange, HUH? I must admit before this revelation, I replaced headlight switch and brake switch, with no avail.
probably the fuse is blown.
The BOO (Brake On/Off) Switch may need to be replaced. If it is bad, it would cause the brake lights to NOT illuminate when the brake pedal is applied.
If you are referring to the brake lights it is probably a bad brake light switch. Your vehicle may also have daytime running lights which would be on without the parking lights.
If you have recently replaced the taillight/brakelight bulbs... you may have installed the wrong type. This will cause the circuit to cross and light up both filaments, which would look like a brake light.
More than likely it is the brake light switch that is attached to the brake pedal.
I would replace the headlight switch as Ford has had their share of these problems.
Check your brake light switch at hte brake pedal.
Low beams are burned out.
brake switch located on the top of the brake pedal
that sounds like i ground in the bake by the lights or if it has a trailer plug i would start their
The most likely cause is a bad brake light switch (if none of the brake lights illuminate) but if its only one of the brake lights, try changing the bulb. Even if they still work as running or turn lights because they have a double filament and may still work partially, but not as brake lights.
I might start by checking the ground wire of the taillight assembly. Make sure there isn't any rust that is preventing a good electrical connection to the chassis ground.
Bad socket? Bad ground? Problem in steering column switch?