SMT CPR ACFT ON FINAL APCH WAS GIVEN RWY CHANGE CLOSE IN AND FLC BECAME SLIGHTLY DISORIENTED ON FINDING THE NEW RWY DUE TO DUSK AND LIGHTING CONDITIONS. TWR LCL CTLR PROVIDED VECTORS FOR THE FLC.

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WE WERE CLRED BY ORD APCH FOR THE VISUAL APCH TO RWY 22L AT ORD; AND SWITCHED TO ORD TWR. UPON INITIAL CONTACT WITH ORD TWR; WE WERE TOLD; 'WE'RE GOING TO SWITCH YOU TO RWY 27R; CONTACT THE TWR ON (NEW FREQ).' I ACKNOWLEDGED THIS AND; BELIEVING THAT WE WERE S OF THE FINAL APCH PATH TO RWY 27R; BEGAN A R TURN TO WHAT I BELIEVED TO BE A L BASE FOR RWY 27R. SIMULTANEOUSLY; I SWITCHED TO THE NEWLY ASSIGNED TWR FREQ AND RPTED ON; WITH THE FURTHER NOTE THAT WE HAD BEEN SWITCHED TO RWY 27R. THE NEW CTLR ASKED IF WE HAD THE ARPT IN SIGHT. I REPLIED THAT WE WERE CONFUSED AND NEEDED ADDITIONAL ASSISTANCE. HE GAVE US A L TURN TO HDG 180 DEGS AND THAT WOULD PUT US ON A R BASE FOR RWY 27R. WE DID SO; PICKED UP THE RWY; AND WERE CLRED TO LAND UNEVENTFULLY. DURING THE MANEUVERING; THE TCASII INDICATED TFC N 1 NM AWAY AND 300 FT BELOW US; ON FINAL FOR RWY 22R. AFTER LNDG; THE COPLT INDICATED THAT HE HAD SEEN THIS ACFT; BUT I HAD NOT; BECAUSE I WAS TRYING TO FIND THE RWY. FACTORS LEADING TO THIS SIT: 1) DUSK; WITH RWY LIGHTS ON LOW AND INDISTINGUISHABLE IN THE 'SEA' OF ARPT LIGHTING; HAZE ALSO PRESENT. 2) CHANGE TO ANOTHER RWY; CLOSE IN; WITH NO HEADING GUIDANCE; AND A CHANGE TO A NEW LCL CTLR. 3) PLT ACCEPTANCE OF AN AMENDED RWY; WHEN IT WAS NOT CLRLY VISIBLE; WITH POOR LIGHTING CONDITIONS. 4) MULTIPLE LNDG RWYS; WITH INTERSECTING COURSES AND DIFFERENT LCL CTLRS. THE SIT WAS DETECTED/CORRECTED BY THE CTLR'S QUERY WHETHER WE HAD THE NEW RWY IN SIGHT; AND MY CONFESSION TO BE CONFUSED AND NEEDING FURTHER ASSISTANCE. I HAVE OPERATED TO/FROM ORD FOR SEVERAL DECADES; WITH NO PROBS/LOSS OF SITUATIONAL AWARENESS. HOWEVER; THIS WAS THE FIRST TIME THAT A SWITCH IN LNDG RWYS AND TWR FREQS WAS GIVEN; CLOSE-IN; AND IN POOR LIGHTING CONDITIONS. I BELIEVE THAT THE CTLRS ASSUMED THAT HAVING THE ORIGINAL RWY IN SIGHT MEANT THAT I COULD SEE ALL RWYS CLRLY; WHICH (AGAIN) I COULD NOT. IN THE FUTURE; I WILL EITHER NOT ACCEPT THE NEW RWY; OR REQUEST A HEADING TO GET PROPERLY ALIGNED. THE THINGS THAT 'SAVED THE DAY' IN THIS CASE WERE THE CLOSE MONITORING BY THE LCL CTLR; THE QUICK CONFESSION OF CONFUSION BY THE FLC; AND THE EXCELLENT REVISED CLRNC/GUIDANCE BY THE CTLR.