MD80 CREW TRIED TO INTERCEPT THE LOC WITH A VOR FREQ TUNED IN.

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WE CAME OUT OF HOLDING TO PAPPI INTXN THEN VECTORS TO FINAL. IT WAS HAZY AND WE RECEIVED VECTORS FOR ILS RWY 27R AT ORD. WHILE PREPARING FOR THE ILS RWY 27R; WE WERE GIVEN TFC GOING TO THE ILS RWY 27L. I WAS DISTR AND NEVER DIALED IN THE LOC FREQ TO RWY 27R. I WAS ON ORD VOR FREQ 113.9. SO WHEN I ARMED THE LOC TO CAPTURE; IT ACTUALLY ARMED THE VOR. I SAW THE ANNUNCIATION IN THE FMA BUT WAS CONCENTRATING ON THE TFC. ALTHOUGH HE WAS CLOSE HORIZLY; WE APPEARED TO HAVE GOOD VERT SEPARATION. HAVING BEEN IN OTHER PARALLEL ILS SITS AND OTHER SITS OF CLOSE PROX TO OTHER ACFT; I WAS NOT CONCERNED. ALSO; THE FO SAID HE HAD IDENTED THE LOC FREQ AND I DID NOT DOUBLECHK AT THAT MOMENT. I NORMALLY VERIFY ALL IDENTS. I THEN LOOKED AT MY FMA AND SAW THE VOR TRACK ANNUNCIATION AND REALIZED MY MISTAKE. I CORRECTED AND IDENTED THE PROPER FREQ AND TURNED 30 DEGS TO GET ON COURSE. WE LANDED UNEVENTFULLY. ATC ASKED US IF HE HAD CLRED US FOR THE APCH OR JUST TO INTERCEPT LOC SHORTLY BEFORE WE FOUND OUR MISTAKE. ATC DID NOT ADVISE US IF WE CAUSED A CONFLICT OR NOT.