I would check to see if part of the brake pedal assembly is rubbing on the wiring. May have worn thru the insulation and completes the circuit when the pedal rubs against it. Or  if the engine runs rough when you hit the brakes, it could be a vacuum leak(power brakes only), and causing idle to drop or stumble and oil pressure to drop. At any rate, the only reason for that lite to come on during operation are over heating and/or low oil pressure.