1998 international 4700 dt466. Having issues with the brake booster. Brake pressure light is on. With key off, press pedal and nothing at all. Hard pedal and backup motor does not come on. Turn key to on position and backup motor comes on. Start engine and motor does not shut off at all. Master cylinder is new, differential pressure switch is new. Flow switch and relay I took off another truck that was working properly. Still no change
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