I've had this problem on my 91 for a while now. Light stays on dimly ever after the e-brake is off. There is a definite change in the brightness with it on and off. Every once in a while the light will go off completely too. I have replaced the pads and the rotors, and put in a new m/c but it didn't change. I was told it could be the sensor in the resovoir cap but I haven't got around to changing it.

91 SR5 Xtra Cab, 298000km, 4" lift, 56" rear springs, 33-12.5R15 BFG Mud-Terran T/A KM2.....and an '85 axle still waiting to go in.