A B737-300 WAS DISPATCHED WITH THE CAPT'S PITOT INPUT TO THE AIR DATA COMPUTER DISCONNECTED.

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AT APPROX XA30 FEB/XA/98; I WAS ASSIGNED ACFT YYY (A COMMERCIAL PAX B737-300 TURBOJET) TURN-OVER FROM PRIOR SHIFT MAINT. THE PLT WRITE-UP WAS THEY WERE GETTING AN 'ATT' FLAG IN THE CAPT'S ADI (ALT DIRECTOR INDICATOR) DURING CLBOUT. THE PRIOR SHIFT A&P MECH REPLACED THE L IRU (INERTIAL REF UNIT) BUT DID NOT FIX THE PROB. ON MY SHIFT I TROUBLESHOT THE PROB TO THE L DAA UNIT (DIGITAL ANALOG ADAPTER); BUT OUR STATION DID NOT HAVE ONE IN STOCK. I SWAPPED THE R DAA UNIT WITH THE L DAA TO VERIFY THAT THE L DAA WAS IN FACT FAULTY. IT WAS. WHILE SWAPPING THE L DAA UNIT WITH THE R DAA UNIT I ACCIDENTALLY MUST HAVE DISCONNECTED THE FLEX LINE TO THE AIR DATA COMPUTER. BEFORE I CLOSED THE ELECTRICAL BAY DOOR; I LOOKED AROUND THE AREAS THAT I WAS WORKING AND EVERYTHING APPEARED TO BE IN PLACE. I WAS DONE WITH MY SHIFT AT XI00. AT APPROX XJ45 ACFT YYY WAS ON TKOF ROLL. THE CAPT NOTICED HE HAD NO AIRSPD INDICATION AND ABORTED TKOF AND RETURNED TO GATE. THE MECHS ON THE DAY SHIFT FIXED THE PROB AND THE ACFT DEPARTED WITH NO FURTHER INCIDENT.