Classic/Antique Car Repair: Brake light stays on when car is turned off., Mopar A body brake warning light

Question
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.
(The body, underneath and engine are excellent shape.  The car has factory A/C that blows cold.  Only the radio does not work, it lights but does not play. The antenna wire is in properly.)
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.
---The brake fluid in the master cylinder is OK.  The four drum brakes are OK.  There is some kind of draw when the key is turned off.  Hope you can help. The mechanics I have asked don't know and suggest pulling the dash to check all wires.  I believe this could cause more problems.
Suggestions please!

Answer
Hello Tom,

The "Emergency Brake Light" actually serves two purposes. The obvious one is as an emergency brake indicator  but also as a low brake fluid pressure warning light. In my experience, you can have one half of your master cylinder bsd and have this light activate, sometimes intermittently while the car will still stop, although somewhat slowly.

Braking performance not as good as it used to be? Pedal going way down to the floor? You might be braking with only the rear drums. Other things can be the cause, but these are the symptoms of a failing master cylinder.

Actually, I feel this could be a combination problem. The actuation of the light by the emergency brake is done simply by a push button mechanical switch making physical contact with the emergency brake rod underneath the dash. After 45 years, this switch can be dirty and intermittent in it's release causing the brake light to stay on also.

I think if you checkout these two paths, you'll find your problem and not have to pull the dashboard either.

With all due respect to your mechanics, pulling the dash for this type of problem strikes me as overkill because they don't understand the system. Unless you have other major wiring problems, this solution seems extreme. Check with your local MOPAR club. They're a cool bunch of young and old guys(like me)who worked on A-bodies back in the day and today. They'll steer you right (and maybe even help you fix it!)

Good luck,

Bob