Let's start with the simple stuff and work our way through it. Start with the switch at the parking brake pedal. First, make sure it is seated in its holder and hasn't moved out of place and that the wiring is intact.
With the ignition switch off, disconnect the parking brake switch and then turn the key on. If the light is on then it isn't the switch, if the light is off replace the switch
If the switch is good, then the next stop is the brake fluid level sensor at the master cylinder.
Again, with the key off, disconnect the brake fluid level sensor, connect a 5amp fuse between tan/light green striped wire and dark green/yellow striped wire and turn the key on. With the key on and the light off, replace the fluid level sensor.
That should get you going for now. After that it will be the wheel speed sensors and possibly some dirt or some other foreign matter caught between it and the wheel.