A DHC-8 WAS DISPATCHED WITH AN INCORRECT WARNING LIGHT MODULE INSTALLED ON THE MASTER CAUTION LIGHT PANEL.

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I WORK LINE MAINT FOR ACR. ON MAY/XA/98 I WAS TOLD THAT ACFT XYZ HAD CAUTION LIGHT PANEL PROBS. MAINT CTL GAVE ME A CLASS CTL NUMBER FOR A NEW CAUTION PANEL IN PARTS ROOM. I WAS TOLD TO GO TO THE GATE AT XX35 AND REMOVE AND REPLACE IT. THE ACFT HAD A DOWN TIME OF ONLY 20 MINS; SO I HAD TO WORK FAST. WHEN THE PLANE ARRIVED; I LOOKED AT THE LOGBOOK AND THERE WAS NO OPEN WRITE-UP; SO I MADE THE WRITE-UP THAT THE CAUTION PANEL NEEDED TO BE REPLACED. ONCE I INSTALLED THE NEW CAUTION PANEL; I STARTED TO REMOVE THE OLD CAUTION PANEL MODULES ONE BY ONE AND INSTALL THEM ON THE NEW PANEL. WHEN I GOT TO MODULE #9; I NOTICED THE PINS THAT HOLD IT IN PLACE WERE BROKEN. SO INSTEAD OF IGNORING THE PROB LIKE THE MECH BEFORE ME BY DUCT TAPING IT IN; I LOOKED AT THE PART NUMBER ON IT AND CALLED MAINT CTL TO ORDER ME A NEW MODULE. WHEN I RECEIVED THE NEW PART; I LOOKED AT THE ROTATABLE TAG TO MAKE SURE THE PART NUMBERS MATCHED; INSTALLED THE MODULE ON THE CAUTION PANEL; AND MADE SURE THE LIGHTS WORKED. I FINISHED THE JOB; SIGNED OFF THE JOBS 1) INSTALLING THE PANEL AND 2) INSTALLING THE MODULE. ON MAY/XB/98; IT WAS BROUGHT TO MY ATTN BY QUALITY CTL THAT I INSTALLED THE WRONG MODULE. THE ONE I INSTALLED HAD A BLANK FILTER; BUT SHOULD HAVE HAD A CAUTION LIGHT FOR THE #2 HYD ISOLATION VALVE. I FOUND THE OLD PART AND ROTATABLE TAG AND SHOWED THEM TO MY CHIEF INSPECTOR. THE PART I REMOVED HAD THE PRE-MOD PART NUMBER; BUT SHOULD HAVE HAD THE POST MOD NUMBER. I FELT I DID MY JOB CORRECTLY. ON THE LINE YOU DON'T HAVE TIME TO GO TO THE SHOP AND LOOK UP PART NUMBERS. I RELIED ON THE PART NUMBER THAT CAME OFF THE OLD CAUTION LIGHT MODULE; AND IT FIT CORRECTLY. IF I HAD ANY REASON TO DOUBT THAT I WAS DOING SOMETHING WRONG; I WOULD HAVE STOPPED WHAT I WAS DOING. THE COMPANY HAS TO DISCLOSE TO THE FAA THE SIT.