ACR MLG RETURN LAND AT SJC WHEN RIGHT MAIN GEAR DOORS WOULD NOT CLOSE WITH GEAR RETRACTION.

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ON SEPT; F/O AND I DEPARTED SAN JOSE FOR SAN DIEGO. UPON LNDG GEAR RETRACTION THE RIGHT MAIN LNDG GEAR INDICATOR LIGHT REMAINED RED/UNSAFE. I REQUESTED THE GEAR BE LOWERED WITH ALL 3 SUBSEQUENTLY INDICATING GREEN/SAFE; AND THEN AGAIN RETRACTED WITH THE RIGHT MAIN GEAR ONCE AGAIN SHOWING RED/UNSAFE. AGAIN; I ASKED THE GEAR BE LOWERED AND AGAIN; RECEIVED A GREEN/SAFE INDICATION; AT WHICH TIME THE GEAR WAS LEFT IN THE 'DOWN AND LOCKED' POS. I MENTALLY CONCLUDED SINCE THERE WAS NO ADVERSE YAW OR HEAVY BUFFETING THAT THE PROB WAS EITHER A) A LNDG GEAR DOOR NOT CONNECTED OR B) A MISALIGNED/MISADJUSTED SENSOR MICROSWITCH; HOWEVER; NOT BEING ABLE TO DETERMINE WHICH CONDITION ACTUALLY EXISTED; A RETURN TO SJC WAS INITIATED. DEP CTL WAS IMMEDIATELY INFORMED OF OUR DIFFICULTY AND ASSISTED WITH VECTORS FOR THE ILS TO 30L AND ALERTING THE EMER EQUIP I REQUESTED TO BE STANDING BY. FLT ATTENDANTS WERE NOTIFIED ALONG WITH THE PAXS THAT A RETURN TO SJC WAS NECESSARY DUE TO 'A MINOR' COCKPIT WARNING LIGHT ILLUMINATION; HOWEVER; FLT ATTENDANT 'A' WAS INSTRUCTED SPECIFICALLY NOT TO PREPARE THE CABIN FOR AN EMER LNDG BUT TO FOLLOW NORMAL LNDG PREPARATION PROCS. UPON ARRIVING AT GATE; THE MAINT LEAD STATED THAT THE RIGHT MAIN LNDG GEAR DOOR HAD NOT BEEN PROPERLY RECONNECTED LAST NIGHT UPON COMPLETION OF CHANGING THE RIGHT MAIN OUTBOARD TIRE. HE FURTHER STATED THAT THE MECHANIC RESPONSIBLE FOR THE WORK HAD OMITTED THIS ON PREVIOUS OCCASIONS AND THAT HE WOULD GET THE MAINT SUPVR. THE MAINT SUPVR INFORMED ME THAT THIS MECHANIC HAD BEEN ADVISED/COUNSELED REGARDING HIS WORK; THAT THIS WAS THE LAST ERROR THEY COULD AFFORD TO ALLOW HIM TO MAKE AND THAT HE WOULD TAKE STEPS TO INSURE PROPER DISCIPLINARY ACTION WAS TAKEN. I QUESTIONED MY F/O REGARDING HIS EXTERIOR WALK AROUND PROCS AND HE ASSURED ME THAT THE LNDG GEAR DOOR APPEARED NORMAL; ALTHOUGH HE DID NOT SPECIFICALLY ATTEMPT TO LIFT OR MOVE THE DOOR. THE DOOR WAS RECONNECTED WITHIN 2 MIN AND UPON RECEIVING A NEW; AMENDED DISPATCH RELEASE; WE AGAIN DEPARTED FOR SAN DIEGO.