I have a 98 Villager and I had the same problem. I found that the brake light switch at the brake pedal needed adjusting. Just loosen the lock nut and adjust the switch so that the brake lights do not stay on but only come on when the brakes are applied, then tighten the locknut. Worked for me. Hope this helps.
brake light switch would be most common cause
fuse, bulbs
Possible ground issue at the taillights.
BAD BRAKE LIGHT SWITCH AT TOP OF BRAKE PEDAL
There is a switch down at the brake pedal, It's most likely bad. This is true. There is a switch under the brake pedal that probably needs to be adjusted or replaced. I have this same problem in my 1998 mercury villager. I have not replaced or adjusted the switch...not sure the cost or how hard it is to do. However, I have found that once you are in park, if the brake lights do not go off, I press down hard on the brake pedal and the lights go off.
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.
More than likely it is the brake light switch that is attached to the brake pedal.
Check your brake light switch at hte brake pedal.
you may have wires crossed if some one has installed a new radio system recentley My Villager did this a couple of years ago. After countless hours in the shop it ended up being the rear taillight. The lead contacts on the bulbs were touching one another and shorting the system.
brake switch located on the top of the brake pedal
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.
Check the switch adjustment on the brake pedal arm.