Brake Light Stays On

[Blue_Bonne]

My 94 bonneville brake light stays on when im driving and just dings until i cut the car off... my brake fluid is full. When i drive my brake would be off. What could be the problem?

[renchjeep]

I am assuming you are talking about the red "brake" warning light on the dash. Here is where I would start:

Sunk float in master cylinder reservoir, bad sensor or wiring/connection at reservoir bottom, parking brake pedal not releasing all the way, bad parking brake warning light switch.

[willwren]

In other words, things that would tell you not to drive the car until it's fixed. It's very likely master cylinder related. Is there any sign of leaking fluid on the booster or down the firewall?

[Blue_Bonne]

I am assuming you are talking about the red "brake" warning light on the dash. Here is where I would start:

Sunk float in master cylinder reservoir, bad sensor or wiring/connection at reservoir bottom, parking brake pedal not releasing all the way, bad parking brake warning light switch.

Yea its the brake warning light...

In other words, things that would tell you not to drive the car until it's fixed. It's very likely master cylinder related. Is there any sign of leaking fluid on the booster or down the firewall?

I have no type of leakage

[skregal]

If you unplug the sensor at the bottom of the master cylinder and the light
goes off, you call rule out the parking brake.

That sensor is built into the master cylinder and cannot be replaced separately,
I believe.

If there are no leaks and level is good, the sensor may be bad.

Mine has been unplugged for 3 years for that reason, but I would
not recommend that, unless you are very in-touch with your vehicle.

[Blue_Bonne]

so i would have to replace the whole master cylinder if the sensor is bad?

[skregal]

I think that is correct. Someone else should confirm.

[Blue_Bonne]

I love bonnevilles and 3.8s I expect to replace parts on a 94 with 165k but geee... breaking my pockets lol. But I got to do what I got to do.

I still havent found any problems I really dont wanna pay someone to look at it and fix it

[willwren]

You need to measure your master cylinder for length from the flange that attaches it to the firewall. There are two different lengths.

One is 6 7/8", the other is 8". I'd suspect you have the shorter (mine is longer than yours ) but measure to be sure.

[renchjeep]

I love bonnevilles and 3.8s I expect to replace parts on a 94 with 165k but geee... breaking my pockets lol. But I got to do what I got to do.

I still havent found any problems I really dont wanna pay someone to look at it and fix it

Just bought a new, not rebuilt, master cylinder for my 94 se from Autozone for $54.95. Bench-bled it, then bled entire system using Prestone Synthetic DOT 3 fluid. My brakes have never felt better!

And, yes, the sensor is built into the reservoir.