FO OF A B737-500 OVERSHOT FINAL DURING A NIGHT VISUAL APCH RESULTING IN THE CAPT TAKING OVER AND ROLLING THE ACFT BACK TOWARD APPROPRIATE PARALLEL RWY. THE FO MISTAKENLY WAS FOLLOWING AN ACFT TO ANOTHER SET OF PARALLEL RWYS.

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ON DOWNWIND FOR RWY 24R AND TOLD TO EXPECT BASE TURN 5 MI PAST SMO. WE CONFIGURED ASAP TO GEAR DOWN AND FINAL FLAPS WHILE STARTING BASE TURN. WE WERE HIGH AND APCH POINTED OUT OUR TFC TO FOLLOW WAS AT 12 O'CLOCK WHEN I SAW THE TFC AND POINTED IT OUT TO THE COPLT. WE WERE CLRED THE VISUAL APCH AND AFTER LOOKING AT THE TFC; I KNEW THAT WE COULD NOT CATCH UP WITH THE TFC; SO I SET UP THE FO ON APCH AND GAVE HIM A 30 DEG INTERCEPT HDG WHILE ARMING APCH MODE AND THEN POINTED TO THE RWY. THE COPLT SAID HE HAD RWY IN SIGHT AND THEN APCH SAID CONTACT TWR. I WENT 'HEADS DOWN' AS THE PNF TO TUNE TWR FREQ AND WHEN I CAME BACK UP TO LOOK OUTSIDE I SAW TFC AT 11 O'CLOCK. I ASSUMED WE HAD ROLLED OUT ON FINAL AND WAS WATCHING THE TFC LINED UP ON WHAT ENDED UP BEING RWY 25L/R. I ASKED TWR IF THIS TFC WAS FOR THE L OR R RWY WHEN TWR SAID IT APPEARED WE WERE DRIFTING L OF COURSE AND THAT THE TFC WE SAW WAS FOR THE S COMPLEX. I THEN LOOKED TO MY 1 O'CLOCK POS AND SAW THE N COMPLEX; TOOK CTL OF THE ACFT; AND MADE AN IMMEDIATE R CORRECTIVE TURN. WHEN I MADE THE CORRECTIVE TURN WE WERE 1/2 WAY BTWN RWY 24L AND RWY 25R. THIS ALL HAPPENED DURING AN IOE WITH A NEW FO AND I WAS THE LINE CHK AIRMAN. THE FO WAS HAVING PROBS AND MY WORKLOAD WAS HIGH DUE TO A SLAM DUNK BY APCH AND MULTIPLE TFC IN PATTERN. ALTHOUGH THE FO SAID HE HAD THE RWY IN SIGHT AND WAS IN A R TURN TO INTERCEPT FINAL; I WENT HEADS DOWN AND DID NOT NOTICE HE ROLLED OUT OF THE TURN TO FOLLOW THE S COMPLEX TFC.