I don't know if this has been fixed or not, but I had the same problem on my '93.
I had to remove the switches that the brake pedal lever actuate, and I found some kind of conductive crud made the brake light stay on. Dremelled the crap out of it, works like a champ.
You say you replaced the switches? Try going to the switches again, but send + 12v to the brake-light side of the switch. Teh puropose is to eliminate the switch as the problem. If the brakes light up, then you have
another bad switch. If it stays off, then leave the + wire connected, but look at other components down the line from the switch. I don't think it's a fuse if the 12v to the switch doesn't do anything.
As a last resort, run + 12v
DIRECTLY to one of the brake light bulb + inputs. That will *definitely* light it up, unless the whole problem is a bad ground (or bad bulb, but not likely unless you burned ALL FOUR out, which I doubt).
-keith