AN MD80 ON INITIAL CLB AT 3000 FT HAD A R ENG INTERMITTENT FIRE WARNING CAUSED BY AN IMPROPERLY CONNECTED FIRE WARNING LOOP.

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ACFT WAS DISPATCHED WITH AN MEL ON LOOP B OF R-HAND ENG FIRE DETECTION SYS. ON CLBOUT I (I WAS PNF) NOTICED THE MASTER CAUTION LIGHT FLICKER; BUT I WAS UNABLE; AT FIRST; TO DETERMINE THE EXACT LIGHT. HAPPENED AGAIN AND 'FIRE DETECT LOOP' LIGHT STAYED ILLUMINATED FOR A FEW SECONDS WITHOUT T-HANDLE ILLUMINATING. FLICKERED AGAIN AND FIRE WARNING. T-HANDLE SOUNDED INTERMITTENTLY. TALKED TO COMPANY AND AGREED TO RETURN TO SEA. QRH WAS FOLLOWED FOR LOOP FAILURE. THE MEL'ED LOOP TESTED FINE AND THERE WAS NO FIRE WARNING WITH B SIDE SELECTED. DID WE HAVE A FIRE OR BLEED LEAK AND RUN THE WRONG CHKLIST? POSSIBLY; BUT IT SEEMED LIKE A LOOP PROB BECAUSE THERE WERE NO OTHER INDICATIONS OF FIRE. THERE WERE SEVERAL MINS BTWN 'FLICKERS;' THE 'A' SIDE FAILED THE TEST AND THE 'B' SIDE TESTED OK; AND THIS 'FLICKER' HAPPENED TO OTHER CREWS RECENTLY. BUT PERHAPS WE SHOULD HAVE FOLLOWED THE FIRE CHKLIST; BUT AGAIN IT WAS INTERMITTENT AND DO WE SHUT DOWN AN ENG IN THIS SIT? WE CHOSE NOT. ON THE GND; THE MECHS FOUND 1 LOOP TO WORK AND TEST FINE BUT THE OTHER WAS FAULTY. THEY ALSO SAID THEY HAD BEEN TROUBLESHOOTING THE PROB FOR 2 NIGHTS AND MAYBE THE WIRES WERE CROSSED. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR STATED MAINT RPTED THE FAILED INTERMITTENT LOOP WAS 'B' LOOP BUT THE CONNECTORS ON THE ENG LOOP WERE SWAPPED FOR TROUBLESHOOTING AND NOT RETURNED TO NORMAL SO THE INTERMITTENT LOOP WAS CONNECTED TO LOOP 'A' CTL PANEL. THE RPTR SAID THE ONLY OPERATIVE LOOP WHICH WAS 'A' LOOP WAS CONNECTED TO THE CTL PANEL 'B' LOOP AND DEFERRED AS INTERMITTENT. THE RPTR SAID THE LOOP 'A' TESTED OK BUT WERE ACTUALLY CHKING THE INTERMITTENT LOOP 'B' BECAUSE OF THE CONNECTOR SWAP.