A B737-400 WAS DISPATCHED IN NON COMPLIANCE WITH THE INCORRECT FO'S HORIZ SIT INDICATOR INSTALLED.

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ON ACFT XXX FLC RPTED THAT FLYING IN NAV (FMC) MODE FO'S HSI CDI NEEDLE FROZE WITH NAV FLAG IN VIEW (INTERMITTENTLY). I WAS ABLE TO DUPLICATE PROB ON GND AND VERIFIED PROB WAS DUE TO A BAD HSI (NEEDLE/FLAG INTERMITTENTLY STICKING). I REMOVED THE FAULTY HSI TO GAIN ACCESS TO ACR PORT #XXXX HSI WHICH I FOUND WAS NOT IN STOCK AT ZZZ. I MADE NUMEROUS CALLS TO OUR MAINT CTL FOREMAN IN ZZZ1; BUT WAS UNABLE TO GET ANYONE. I NOTIFIED THE MAINT TWR COORDINATOR HERE IN ZZZ OF THE SIT AND HE SAID HE WOULD GET PROPER AUTH TO ROB AN HSI FROM ANOTHER ACFT. I GAVE HIM THE ACR PART NUMBER XXXX AND CONTINUED TO WORK THE 4 OTHER ACFT THAT CURRENTLY HAD AVIONICS WRITE-UPS. LATER I WAS CONTACTED BY OUR MAINT TWR COORDINATOR WITH AUTH OF OUR MAINT DUTY MGR TO ROB THE FO'S HSI FROM ACFT YYY. I WAS ALSO GIVEN A ROB AUTH CTL NUMBER ISSUED BY THE MAINT DUTY MGR WITH STORES (THE DEPT RESPONSIBLE FOR PARTS). I REMOVED THE PART FROM ACFT YYY; MADE A LOGBOOK ENTRY - FO'S HSI REMOVED FOR XXX AND COMPLETED THE ROBBED PART TAG. I INSTALLED AND COMPLETED A SATISFACTORY OPERATIONAL CHK OF THE FO'S HSI ON XXX AND REMOVED THE ACFT FROM CAT II/IIIA PER OUR MPP PROCS. PLEASE NOTE THERE WAS NO ACR PART PLACARD ON THE ROBBED HSI AND I HAD TO USE THE MANUFACTURER SERIAL NUMBER FOR THE INSTALLATION PAPERWORK. THE ACFT WAS THEN DISPATCHED FOR REVENUE SVC. I WAS NOTIFIED 3 DAYS LATER THE PART REMOVED FROM ACFT YYY WAS THE WRONG EFFECTIVITY FOR ACFT XXX AND WAS LATER REPLACED WITH PART NUMBER XXXX THAT I ORIGINALLY REQUESTED.