brake warning switch

Exactly. In front disk cars, it is termed "combination valve". In drum cars, a "distribution block". Both have the "imbalance warning" switch, since ~1968. Either that switch or the parking brake switch can short to ground, causing the lamp to light.

My 1996 Voyager is the same (even w/ ABS added to the combo valve), but adds a 3rd "MC reservoir low fluid" warning switch. Any of the 3 can short to ground to light the lamp. I recently dug thru that when the light stayed on after a fluid refresh and poor info in the manuals. Turned out to the reservoir float had stuck. I expect all 1990's Mopars were the same. If you change to a later MC w/ level sensor (as I did), you now know how to simply wire it in to also light that lamp.