[sokoloff]

Every car I've worked on over the last 3 decades has a brake fluid level sensor (usually just a go/no-go float switch).

https://www.youtube.com/watch?v=jsGZJFMgUpA has a quick view to it on a random car in the first 11 seconds of the video.

(Something very much like) This is required by 49 CFR §571.135.S5.5

https://www.law.cornell.edu/cfr/text/49/571.135

[calvinmorrison]

yeah what.... it's literally just a float switch wired to the dash light