Brake fluid reservoir is back against the firewall, right above the brake pedal but in the engine compartment. There's a float switch in the cap, you'll see a couple wires coming from it.

If you check & it's full, unplug the wires for a day or 2. If the light never comes on then it's probably a flaky float switch.

The other thing that light does is a handbrake reminder. There's a little button switch under the brake handle. Sometimes that's flaky or bent or something. If that's the problem your light will still come on even when you unplug the wires at the brake fluid reservoir.