Cusser
+1y
I'm siding with Dan on this one, that's the one involved with what you did here.
The brake light is actuated by that floating magnet/sensor being too low, the handbrake being left on, or the "normally open" switch down on the pedal assembly.
So if the fluid level in the master cylinder reservoir is at correct level (and the sensor in place), and you engage/disengage the handbrake lever several times, about the only thing left would be to check out the brake pedal switch.