OT?

My 2000 Toyota Solara convertible started displaying the Brake light on
the instrument panel a few months ago. It wasn't a parking brake
problem. It would go on for a couple minutes and then go off for an
hour, for example. Sometimes it would go on when I was cruising on the
highway and not using the brake.

The master cylinder was full. Well, it was maybe 1/4" low so I bought
some brake fluid (old brake fluid is supposed to be bad. It absorbs
water, so it's especially bad if you have anti-lock brakes, which iirc
have parts that can rust.)

I couldn't see the opening while pouring, only the front part of the
chamber through the milky plastic, where the level was lower, so I
filled it to the brim and when I put the cap on, it overflowed through
the hole in the cap.

That was 3 weeks ago and the light hasn't been on since. The counter
guy at Pep Boys said the same thing, that his light was on and only one
ounce of fluid to fill it up was enough to turn off the light.

No wires go to the cap and no evidence of anything in the top inch and a
half or more of the master cylinder to turn the brake light on if the
fluid level is low. I don't know why this worked.