it's a turn switch - the one you use to indicate the turns

and switch between near and far light.
It's mounted on the left side of the steering column and,
as I said, it's a kind of difficult to reach it and unmount.
That's why I recommend testing if this switch is responsible
for brake lights behavior.
I'm 95% sure in that because the problem with the symptoms
you describe has been discussed multiple times here and I
had this problem on my Lumina, too.