5K Brake Warning Lite

[Steve Sherman <spsherm@ibm.net>]

My wife's 86 5KCSTQW just started to show the brake warning lite.  At
least I assume that it is a brake warning lite, triangle with a full
circle in it and some dashed lines on each side of the circle.  Sort of
like a drum brake (although this car has disk on a 4 ;-)

Could folks let me know if I am right about this warning lite, and
(assuming I am) let me know about:

1.  If this a low pad warning, how much longer before it gets
dangerous.  Breaking seems fine now.

2.  What pads do folks recommend for replacements.  I don't need
anything like for a track, OEM types are probably fine.  Most of our
driving is on dirt roads, where the tires to dirt are a bigger limit to
braking than the disk/pad combo.

3. How hard is it to replace the pads oneself?  Do these calipers
pistons twist in with a special tool, or is it an easy push?

TIA

Steve