If you are referring to the brake light then the brake light switch is stuck.
The brake lights on a 96 Jimmy are operated by the brake light switch, mounted on the brake pedal assembly. If the switch is bad the lights could stay on or off, or be sporadic.
The brake light switch is broken or out of adjustment.
brake light switch above the brake pedal
If the bulbs are good then the brake light switch is bad, it's on top of the brake pedal up under the dash.
A bad brake light switch, and it is bolted to the steering column in under the dash.
Check the fuse. Then check the wiring.
try swapping wires on brake light switch--do stop lights work?
brake light switch is bad
Brake Lights Do NOT turn offUsually this is caused by the brake light switch being out of proper adjustment [most likely], but it also could be caused by a defective switch [less likely].
look on top of the brake pedal under the dash and you will see the switch, with one hand push the brake pedal down and with the other hand push the brake switch in as far as it will go in it's holder and then pull the brake pedal back with your hand to set it.
You may need to check your brake light switch. It is a small switch located on top of your brake peddle (up on the arm of the peddle). This switch allows the brake lights to come on whenever you push the peddle.