I have a 87 accord hatchback.

The dash brake warning lamp lights up on the first press of the brake
pedal and stays on until the car is shut down.

The brake pedal feels firm and the brake fluid in the master cylinder
is full (no fluid loss). The car stops fine.

Since the warning lamp lights up on first application of the brake
pedal, I am suspecting a faulty sensor.

What type of sensors trigger this light in an 87 accord?

Any ideas on what the problem could be?

Thanks