Check for a broken or disconnected vacuum hose
replace brake hose they colaspe
A 1991 Jeep Wrangler uses DOT 3 brake fluid.
The brake lights.
Probably a faulty brake light switch or the brake light switch is installed incorrectly.
the brake light
You might have an issue with the 4wd shifter location, and the 93 has a foot brake instead of a hand brake, but it will probably go.
Whether or not the brake and/or gas pedals are pressed, how far they are pressed, & for how long.
when they start to squeek
Dot 3.
fuse, bulbs, switch on brake pedal.
The brake light switch is connected to the brake pedal and the brake linkage under the dash with a single bolt.
red