'92 Sierra Brake Light Problem

I have a '92 Sierra shortbed with a brake light that comes on at 37 miles per hour. I have replaced the brakes myself and have had the local guys look at it but we are all stumped. I have also replaced the master cylinder and reset the computer but the light keeps coming on.Though I can drive all day and it wont come on unless I speed up to 37.This has been going on for 6 months. Please help!

Do you have cruse control? If so it could be something with the cruse control module. Also have you tried to lift the brake pedal when at 37 mph to see if the turn off?

I had the same problem on my 91. It was the rear brake light switch.