If your Blazer has the Electronic Anti-Lock brake controller attached to the master cylinder, unplug it (both plugs) for about 20 seconds and plug it back in. Sometimes I have had to disconnect the battery and unplug the controller to get the light to go off. I had this happen on my '90 FS Blazer (288,000 mi) and the light would come on whenever it wanted to. I had a trailer connector with a bare wire that would sometimes contact the frame and I believe that caused it to activate the light, but that was not all the time. After covering the bare wires it still comes on, but very rarely. Be very sure there is no actual brake problems before dismissing the light totally.