MLG TOLD TO FOLLOW AN MLG ON A VISUAL BUT WEREN'T TOLD WHICH OF 2 MLG'S TO FOLLOW. FOLLOWED WRONG ONE TRIGGERING TCASII RA.

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DSNDING INTO CLE AT 3000 FT ON A R BASE LEG TO RWY 23L APCH CTL ASKED IF WE HAD THE ARPT AND/OR IF WE HAD AN MLG 11-12 O'CLOCK POS. CAPT REPLIED WE HAD THE ARPT AND THE MLG. WE WERE THEN CLRED FOR THE VISUAL APCH TO RWY 23L BEHIND THE MLG AND TOLD TO CONTACT TWR. CAPT SWITCHED TO TWR AND TOLD THEM WE WERE FOLLOWING THE ACR X MLG. TWR SAID THE TFC WE WERE FOLLOWING WAS AN ACR Y MLG; WE THEN LOOKED TO THE L AND FOUND THEM. TWR TOLD US TO TURN TO 050 DEGS WHICH WE DID. AFTER ABOUT 1/2 OF THE TURN; TCASII CALLED FOR A DSCNT WHICH WE DID AND WHEN CLR; WE STOPPED THE DSCNT AND TWR THEN TURNED US TO THE ARPT AND WE CONTINUED THE VISUAL TO RWY 23L. WHEN APCH STATED TFC WAS AT 11-12 O'CLOCK; THAT IS WHERE ACR X WAS EXACTLY AND ACR Y WE DID NOT SEE AT THAT TIME. THEY ALSO DID NOT STATE AN AIRLINE TYPE WHICH WHEN APCH HAS 2 MLG'S FOLLOWING ONE ANOTHER; I BELIEVE SHOULD HAVE BEEN DONE OR AT LEAST MADE US AWARE OF THE FACT THAT THERE WERE 2 MLG'S TO WATCH FOR. I BELIEVE APCH CALLED THE TFC IN THE WRONG POS FOR US TO FOLLOW OR JUST DIDN'T GAUGE ACR Y POS FROM US ACCURATELY.