A DHC8-300 Captain briefed his First Officer; who was previously off the radio; about an ILS Runway XXL approach when the actual clearance was ILS XXR. Through a series of briefings the crew did not detect the error until ATC issued a new clearance.

Narrative

First Officer left frequency to call company in range. During that time; I checked in with Approach. Controller advised to expect ILS XXR. First Officer returned to primary radio; and I advised him that I checked in with approach; and we were to expect XXR approach. Stated that I would brief him on the approach. I pulled out the chart; but it was the wrong one. I stated ILS XXR; but in fact had the chart out for XXL. This was an inexcusable; deplorable error on my behalf. Read out all the numbers for XXL approach. First Officer did not catch mistake. He at this point he must have thought that we were doing the approach for XXL; because I stated XXR during the first word with the briefing header. Because of this; I set the wrong frequency for XXR; as did he. On the base turn; I stated; 'please identify my ILS XXR'. Again; a potential error trap was missed; as he looked at the Morse code for the XXL chart he had on his yoke clip. He stated; 'you're ID'ed'. Controller vectored us for the approach; and stated; 'intercept the localizer XXR.' Yet again; another opportunity to catch the mistake was made. As the LOC needle centered; the Controller queried us. The First Officer replied over the radio; 'I thought that you wanted us to join XXL'. She then vectored us for a XXR intercept and cleared us for the approach. At that point we were about 12 miles out.