91 Park Ave. - Brake Light Coming On

[timrice]

The brake light comes on almost every time I stop, and remains on for a brief period while accelerating after a stop. Then it goes out until the next time I stop. This happened infrequently at first, but it has gotten steadily more frequent, and happens almost 100% of the time now.

It's probably time for some general brake maintenance, but I would also like to understand electrically speaking what circuit(s) or sensor(s) actually make the brake light come on.

I'm going to start looking into it today.

[Shrocat]

The most common thing that causes the light to come on is low fluid. Since it is not on all the time, it probably is indicating that the pads or rear shoes are worn out and the fluid goes dangerously low when applying the brakes.

[tman]

Is he talking about the brake trouble light? I thought he was talking about his stoplights in the taillight assembly, but your method makes better sense.

[Shrocat]

The way it was worded the question could have been taken either way, but it seems far more likely he was concerned about his warning light coming on, rather than his brake lights coming on. :-).

[tman]

I agree with you, but I already had a long, detailed procedure planned for changing the brake pedal position switch!

[timrice]

(D'oh!) I didn't realize how vague my initial post was. I *was* talking about the warning light on the dash, not the brake indicator lights on the rear of the car.

I should also say that upon inspection it did not take long to realize that I needed two new brake cylinders on the rear brakes. Both were leaking badly and crudded up everything in the drum. I put new shoes and cylinders in and cleaned up the drums, bled the brakes, and no more brake warning light.

That said, I still don't know what sensor(s) / circuit(s) made that light came on. Is it just the fluid going down below the level of the sensor that's in the master brake cylinder? (Don't see how, because the fluid was still pretty close to the top despite the leaks.) Anyway, please enlighten me.

Again, sorry for being unclear originally. I'm going to go have a good laugh at myself for that.

[Shrocat]

Sometimes it is easy to not be as clear as you would like. However, I am glad you found the problem, before it caused an accident. And, as far as I know, the 2 things the brake light indicates are the parking brake being on, and low brake fluid. Your fluid level would drop as it was
being forced out of the leaky cylinders, but would come back up as the brakes returned to postion, and the lines filled with air. I think.