it probably has a leak...
you can only fill your brake fluid from the reserve.
For a 1996 Ford Bronco : DOT 3 brake fluid ( meeting Ford specification ESA-M6C25-A )
look at the inside of your rear wheels are they stained and wet ? yes its your rear wheel cylinders if no check where your master brake cylinder is bolted to the round brake booster where they meet is there a trail of fluid where they meet? yes then you have a master cylinder problem if not you can have leaking hydraulic hoses or brake lines. either way get it checked before you hurt yourself or someone else. g
Is the brake fluid level low in your brake master cylinder in the engine compartment ?
According to the 1996 Mercury Cougar Owner Guide : ( DOT 3 brake fluid , meeting Ford specification ESA-M6C25-A )
possibly your hoses. Washer fluid will deteriorate your hoses. Check into that.
It has a hydraulic clutch ( the brake fluid reservoir is also the clutch fluid reservoir )
brake fuild is normally on the drivers side and it is a round canister the fluid will be simi clear maybe a little yellowish it should say in yellow writing what is recomened kind of fluid exp.dot fluid
dot 3
no
sounds like overheating of brake line, either from hot pavement, or cat converter. causes brake fluid to boil and loss of pedal.
If it is an automatic the dipstick is right next to the brake fluid master cylinder reservoir. If it is a stick shift there is not dipstick.