A DC9-10 PA RELAY INTERLOCK BOX WAS FOUND TO BE WIRED FOR ONE AIRPLANE ONLY BUT HAD NO WIRING DIAGRAMS OR SUPPORT DOCUMENTATION.

Narrative

ON OCT/THU/02; A PA INTERLOCK RELAY BOX WAS REMOVED AND REPLACED FOR A CHIME PROB; ON ACFT X. AFTER RELAY BOX WAS CHANGED; A DIFFERENT PROB BEGAN. PA DID NOT OPERATE FROM ANY STATION IN THE COCKPIT; BUT IT WORKED AT THE FORWARD AND AFT ATTENDANT PANEL STATIONS. TROUBLESHOOTING BEGAN FOR SEVERAL DAYS; INCLUDING CHANGING THE RELAY BOX AGAIN; CHANGING WIRES OUT; INSPECTING EVERYTHING AND ANYTHING. FINALLY; ORIGINAL INTERLOCK RELAY BOX WAS FOUND TO BE UNIQUELY WIRED JUST FOR ACFT X. ALL OF THIS WAS DONE BY SEVERAL DIFFERENT TECHNICIANS ON ROTATING SHIFTS. ORIGINAL RELAY BOX WAS RECEIVED ON OCT/FRI/02 AND INSTALLED; BUT THE PROB DID NOT GO AWAY. IT WAS DISCOVERED BY MYSELF AND COMPANY X ENGINEERING THAT ORIGINAL BOX WAS CHANGED. VENDORS APPARENTLY USING WRONG WIRING MAINT MANUALS; PROVIDED BY COMPANY X; CHANGED INTERNAL WIRING. THEREFORE; WHEN WE RECEIVED ORIGINAL RELAY BOX; IT ACTED LIKE ANY OTHER NEW BOX. I KNEW WHAT THE PROB WAS SO; THEREFORE; USING COMPONENT WIRING MANUALS I OPENED THE BOX AND WIRED RELAY BOX TO ORIGINAL CONDITION USING COMPONENT MAINT MANUAL (SUPPLEMENTAL 23-30-2 DATED OCT/XA/02). I INSTALLED THE BOX AND PERFORMED A SYS FUNCTIONAL CHK USING MAINT MANUAL.