itermittant brake warning light/ 05 jimmy

the brake warning light ( on the dash ) is randomly going on and off, even at driving speeds. have had it looked at but no problems could be found. the brakes are fine ,couldn't find any wiring problems. some days it won't even come on at all ,and some days it does with no particular pattern.

Check fluid level in reservoir? If borderline could cause light to come on randomly.....

Other possibility is switch at the e-brake.....could be something as simple as an adjustment.....