check engine light on only when brakes applied
 

89 Mercedes 300 se .check engine light comes on when brake pedal applied.if I start the car the light is off, but when I apply the brake pedal the check engine light stays ON and remains on until I turn off the ignition.light only comes on when pedal is APPLIED,AND REMAINS ON. THE PADS ARE OK.ANYONE ENCOUNTER THIS BEFORE. THIS CAR IS OB1. 8 PIN CONNECTER TEST PORT.NEW 02 SENSOR.