What sets off the brake light?

[Devin]

My brake light has been flickering on and off for a few days. I thought at first it was something to do with fluid level, so I topped it off and it stopped, but then I had a hard braking at one point and the light has been on since then, solid. Any thoughts?

 

[sperold]

Is the reservoir still full?
In the old days, when you could take the top off of the master cylinder (and the reservoir was cast into the assembly), there were 2 chambers in the reservoir. When you had a leak associated with whatever chamber, a brake light would come on to show you that one chamber was dry.
In our cars, the light usually means the plastic reservoir is low, as the lid has a float associated with it.

 

[TimboSHO]

The red brake light will also come on if the parking brake is on, or if the switch is not quite pushed all the way down. Most SHOs have had the rubber pad melt off of the top of the parking brake that actually holds the switch in, leading to the light being on if it doesn't fully retract.

 

[Devin]

Is the sensor attached to the pedal?

 

[Irish Pride]

The sensor is above the parking brake pedal. Lift up on the parking brake and see if the light goes out. The person that had my 91 before me used a very thin bottle cap to glue to the top of the pedal and it's worked fine like that. Never thought about changing it.

 

[rubydist]

another alternative possibility (although remote) is that the little float in the brake fluid reservoir has failed and no longer floats, so the switch is closed even though there is plenty of fluid.