B767-200 CREW HAD AN ERRATIC AND VARIABLE LOC COURSE WHILE FLYING THE LOC RWY 27 APCH AT SAN.

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3 LOC APCHS WERE ATTEMPTED. THE FIRST 2 WERE DISCONTINUED APPROX 5 MI PRIOR TO THE FAF. RADAR VECTORS WERE REQUESTED AND RECEIVED FOR ANOTHER APCH. THE THIRD APCH RESULTED IN AN UNEVENTFUL LNDG. THESE APCHS WERE FLOWN BTWN XA15 AND XA35 WHEN THERE WAS NO OTHER TFC IN THE APCH PATTERN. THERE WERE NO TFC CONFLICTS. ON THE FIRST 2 APCHS; ATC VECTORED OUR ACFT TO INTERCEPT THE FINAL APCH COURSE. AFTER ROLLING OUT ON THE INBOUND COURSE; THE AUTOPLT ATTEMPTED TO TRACK THE LOC. HOWEVER; LARGE COURSE DEVS OCCURRED; REQUIRING MISSED APCHS; WHICH WERE ACCOMPLISHED MANUALLY. THE FMC TRACK PRESENTATION AND THE LOC COURSE DEV INDICATOR PRESENTATION SHOWED CONFLICTING COURSE GUIDANCE. APCH CTL CONFIRMED THAT WE WERE TRACKING L OF COURSE; AS PRESENTED ON THE FMC DISPLAY. THE LOC WAS PROPERLY TUNED AND IDENTED AND THE LOC DME MATCHED THE FMC GENERATED FIXES ALONG THE FINAL APCH COURSE. AFTER THE FIRST APCH WAS DISCONTINUED; I THOUGHT SOME ERROR IN SETTING UP FOR THE APCH MAY HAVE OCCURRED. HOWEVER; FOLLOWING THE SECOND APCH; I SUSPECTED PROBS MAY EXIST WITH EITHER THE ACFT LOC RECEIVER OR THE LOC XMITTER FROM THE GND STATION. ATC ADVISED THAT THE GND STATION WAS MONITORING NORMAL. ALL LOC INDICATIONS IN THE COCKPIT WERE NORMAL. SINCE I HAD EXTRA FUEL; A THIRD APCH WAS FLOWN MANUALLY. FOLLOWING THE TURN ONTO THE FINAL APCH COURSE; LOC GUIDANCE INITIALLY COMMANDED A L COURSE CORRECTION. HOWEVER; SHORTLY THEREAFTER; LOC COURSE GUIDANCE COMMANDED A COURSE CORRECTION BACK TO THE CTRLINE AND STABILIZED FOR THE REMAINDER OF THE APCH. COURSE GUIDANCE WAS COMPARED TO FMC TACK INFO. ADDITIONALLY; COURSE GUIDANCE COMPARED FAVORABLY WITH ADF BEARING INFO (NDB ON THE ARPT) THAT COINCIDED WITH THE LOC FINAL APCH COURSE. ONCE ESTABLISHED; WE WERE ABLE TO DEPART THE VECTORING ALT AND MAKE THE APPROPRIATE STEPDOWN FIXES. LOC GUIDANCE WAS SOLID FROM 2 MI OUTSIDE THE FAF TO THE VDP. THE THIN OVCST LAYER OF CLOUDS (TOPS AT 1000 FT MSL AND BASES AT 800 FT MSL) ALLOWED US TO VISUALLY ACQUIRE THE RWY APPROX 4 MI FROM TOUCHDOWN. I SUBMIT THIS RPT TO HIGHLIGHT THE IMPORTANCE OF USING ALL OF THE ACFT RESOURCES AVAILABLE TO ENSURE A SAFE APCH AND LNDG. IF THE ACFT IS NOT PERFORMING; AS IT SHOULD; DON'T LET ONE'S EGO REPLACE GOOD JUDGMENT -- DISCONTINUE THE APCH AND TRY AGAIN. ALSO; ALWAYS HAVE A BACKUP PLAN. WE LANDED WITH APPROX 40 MINS OF EXTRA FUEL (THE EXTRA FUEL DID NOT INCLUDE OUR RESERVE FUEL OR THE FUEL NEEDED TO DIVERT TO OUR ALTERNATE ARPT). WE HAD ENOUGH FUEL TO FLY A FOURTH APCH; IF NECESSARY (IE; AN NDB APCH TO THE SAME RWY WITH THE SAME WX MINIMUMS AS THE LOC APCH).