Bulb failure DIS

Hi
I have a 1998 A4 2.4SE I have a problem with a brake light failure warning on the DIS I have replaced the lamps disconnected the brake light switch the DIS still shows brake light failure as soon I start the car without my foot on the brake pedal I have read on another post that there are bulb monitoring devices on the relay carrier up in drivers footwell which inform the DIS if there is a bulb blown can any one confirm if this is correct and are they easy to replace any advice would be much appreciated.