Aaand on to my next issue:

I have a '90 automatic Westy.  The brake warning light in the instrument
panel won't go out.  Brake fluid is good (this van has the brake fluid
level sensor cap).  No change (no flicker or anything) regardless of
whether I release the e-brake or press the foot pedal.  I have not tried
driving the van more than a few feet.

What I really need to know short-term is if this could indicate a risk of
brake failure / danger to drive -- I have plans that require the vehicle
today.

I've seen some suggestion that this is just a dummy light ("Dummy, release
your e-brake!") that also illuminates for low fluid ("Dummy, top off your
brake fluid!"), in which case it would seem to not indicate a safety issue
given my fluid level.

But I also read something that seems to say this can happen if there's an
issue with pressure in the master cylinder, which sounds dangerous to me.
 (Disclaimer:  I'm pretty ignorant on this topic.)

The issue does not seem to me to be the little 1-wire button switch thing
at the e-brake itself.  I can get into the diagnostics of the other parts
later, right now I'm really just asking about risk of brake failure so I
can figure out if I need to cancel my plans.

Best,
George