Can't give you an answer to the problem, as it seems all 3 systems don't have a common link, except maybe poor ground. That's not to say a past owner did some creative wiring to the car that causes the problem.
However, the 93 manual has been added recently to the GM service manual thread. Good hunting.
Sounds like you are missing a ground connection on one of the brake lamp bulbs or sockets. With no ground, the current flows through the brake lamp filament and then through the bulb's other (parking) filament to a ground on the parking lamp circuit. Dash lights are on the same circuit as the parking.lights so they light up also. I would pull out the brake lamp bulbs one-at-a-time until you find the culprit, then locate the missing ground for that one.
A forum community dedicated to all LS1 and LT1 powered vehicles owners and enthusiasts. Come join the discussion about performance, specs, builds, conversions, swaps, modifications, troubleshooting, maintenance, and more!