If you mean the switch that puts the brake lights on and off when you step on the brake pedal then it's located where the brake pedal is, can't miss it.
If you follow the brake pedal up under the dash, you'll see the switch where the actuator arm from the brake master cylinder attaches to the pedal.
You need to be more specific What exactly is wrong with your brakes . There are a number of relay's in the brake system .But not neccesarily a fuse . if your brake pedal is hard as a rock (no power brakes) most time its the electric brake booster relay mounted near master cylinder on firewall use dealer relay only only 23 bucks
right above the brake pedal on the left
bad master cylinder
If you mean that you can't shift the shifter while pressing on the brake, I would say that it is down by the brake pedal.
Look to the far left drivers side pedal area and there is a small pedal which is the parking brake which releases when you put the shifter in drive or reverse.
There is only one ABS brake pump motor recommended for the 1990 Lincoln Mark VII. The ABS pump is manufactured by three different companies.
on top of brake pedal, many times the wire breks on plug to switch from flexing
CHECK the brAKE LIGHT SWICTH ABOVE THE PEDAL ANOUT 10 inches ,by chech see rear brake lights work. CHECK the brAKE LIGHT SWICTH ABOVE THE PEDAL ANOUT 10 inches ,by chech see rear brake lights work.
Have you checked the brake fluid level in the master cylinder it may be low causing a light to come on . i did the level is ok.
I would first check your brake light switch which is attached to your brake pedal under the dash. Since you can turn off the lights by pushing the pedal it is possible the switch is bad. They are around $10.00.I hope this helps you. Mark