Dash brake light stays on

My 1972 Valiant emergency brake light (dash-red square light) stays on when I turn the engine off. —— When I turn the engine on, the emergency brake light goes off.
1972 Valiant, 8cyl 318 engine. 96,000 original miles.
Too make sure that the red light does not run the battery down, I take the negative post off the battery when not running the car.
Hope you can help