A B737-300 WAS DISPATCHED WITH THE INCORRECT FMC DISPLAY UNIT INSTALLED.

Narrative

ON OCT/THU/04; ACFT CAME TO THE GATE WITH A #2 ATC CTL PANEL PROB. R&R'ED CONTROLLER AS PER MAINT MANUAL. THEN I WAS NOTIFIED BY THE PLT OF ACFT THAT #2 CDU HAD A PROB TOO. I INSPECTED THE PROB; NOTED THAT THE CLR BUTTON ON THE CDU WAS BROKEN. I WENT TO THE PARTS ROOM AND INADVERTENTLY PICKED UP THE WRONG PART; INSTALLED IT; RAN AN OPS CHK -- CHKED GOOD AS PER MAINT MANUAL. AS OF DEC/THU/04; I WAS UNSURE THAT I HAD INSTALLED PART MENTIONED UNTIL AVIATION SAFETY INSPECTOR NOTIFIED ME IN PERSON AT THE MAINT HANGAR THAT I HAD INSTALLED THE WRONG CDU FOR ACFT X. DURING THE SHORT DISCUSSION; SAFETY INSPECTOR TOLD ME NOT TO WORRY ABOUT THE LETTER OF INTENT. I REPLIED TO SAFETY INSPECTOR I NEEDED TO DO SOME RESEARCH BECAUSE I COULD NOT RECALL CHANGING A CDU DURING THE MONTH OF NOV/04. AFTER A COUPLE OF HRS OF RESEARCH; I FOUND OUT THAT I HAD CHANGED THE WRONG PART BACK IN OCT/04. AFTER REVIEWING THIS EVENT; I DISCOVERED THAT THIS EVENT COULD HAPPEN AGAIN BECAUSE OF THE AMBIGUOUS WORDING OF PARTS CODING SYS.