Chevrolet: 1990 c3500, brake light switch, proportioning valve

Question
i have a 1990 c3500 cheyenne pickup truck with tbi 454 and turbo 400, the problem i am having is with the brake light on the dash. for some reason it is glowing at half brightness all the time. someone told me that it could be a brake service warning light? if so how can i reset it and get it to go away. i have tried disconnecting both the brake light switch and the switch on the proportioning valve but the light keeps glowing.
thanks for your help.

Answer
Hea Matt;
      I wonder , did you look at you brakes do see if they
are going ? also the brake fluid. I would also try to bleed the system and see if it will make the light go out.it is on for a reason and by removing a wire or un pluging it will not remove the condition that might be there. I would check all the brakes and fluid, etc. first OK.Than check the sensor.
Roger