THE FLC OF AN ACR SA226 METROLINER FREIGHTER FOLLOWED THE WRONG B737 ACR DURING A VISUAL APCH CAUSING A LTSS CONDITION.

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ON JAN/TUE/99; MY FO AND I WERE ON A PART 135; REVENUE FLT BTWN BOISE; ID; AND SALT LAKE CITY; UT. TFC FLOW WAS TO THE N AT SLC; AND WE HAD BEEN CLRED AND OPERATING ON THE BEARR 3 ARR; LNDG N. N OF THE ARPT WE WERE CLRED OUT OF 17000 FT DOWN TO 12000 FT -- THE FLT WAS IN IMC FROM 17000 FT UNTIL BREAKING OUT AT 12000 FT. AFTER BREAKING OUT OF IMC CONDITIONS (12000 FT; ABEAM THE FIELD) WE OBSERVED THE FIELD IN SIGHT; RPTED IT AS SUCH; AND REQUESTED THE VISUAL APCH FOR RWY 35. THE CTLR ADVISED TO CONTINUE HDG 155 DEGS AND DSND TO 10000 FT. AT 10000 FT THE CTLR ASKED IF WE HAD A B737 AT 10-11 O'CLOCK POS IN SIGHT AND WE ADVISED THAT WE DID. AT THIS POINT THE CTLR ADVISED US TO FOLLOW THAT B737 TO RWY 34L. WE COMMENCED THE BASE TURN TO FOLLOW THE B737 WHICH WAS PASSING OFF OUR L SIDE. AS WE WERE COMPLETING THE TURN TO BASE THE CTLR ASKED US WHERE WE WERE TURNING TO. WE ADVISED THAT WE WERE FOLLOWING THE B737 THAT HAD PASSED OFF OUR SIDE. AT THAT POINT THE CTLR ADVISED US TO START AN IMMEDIATE R TURN TO A HDG OF 155 DEGS. AS WE WERE TURNING TO 155 DEGS THE CTLR POINTED OUT AN ADDITIONAL B737 AND TOLD US TO FOLLOW THAT B737. AS WE TURNED TO FOLLOW THE SECOND B737 WE ADVISED THE CTLR THAT THERE WAS ANOTHER B737 BEHIND THE SECOND B737. THE CTLR ADVISED US THAT THE B737 IN QUESTION WAS FOR THE OTHER RWY; AND TO FOLLOW THE B737 IN FRONT OF US. THE APCH AND LNDG WAS CONTINUED FROM THIS POINT WITHOUT FURTHER INCIDENT. UPON TAXI OUT FOR OUR RETURN FLT WE WERE ADVISED TO CONTACT TRACON; AND WERE ADVISED LATER DURING THE DAY THAT THE INCIDENT WHICH RESULTED IN A LOSS OF SEPARATION WAS GOING TO BE TREATED AS A PLTDEV. CONCLUSIONS: AT NO POINT IN TIME WERE WE OPERATING WITH THE INTENT TO PUSH OUR POS FOR SEQUENCE TO THE FIELD. IN FACT WE WERE ATTEMPTING TO FOLLOW DIRECTIONS AS DILIGENTLY AS POSSIBLE. AS USUAL; WHEN ANY TYPE OF IMC CONDITIONS OR CEILINGS PREVAIL IN THE SLC AREA; TFC DOES TEND TO GET CONGESTED. PERHAPS IN THE FUTURE; IF POSITIVE SEPARATION IS IN QUESTION; THEN VISUAL APCH CLRNCS SHOULD NOT BE ISSUED. AT NO TIME DID THE CTLR ADVISE US WHAT NUMBER WE WERE IN SEQUENCE FOR LNDG; WE WERE JUST ADVISED TO FOLLOW THE B737. FURTHER; THE CTLR DID NOT ADVISE COLORS; IE; RED ACR B737; BLUE ACR B737; ETC; AND OUR UNDERSTANDING IS THAT THE TA WOULD BE FOR THE CLOSEST ACFT; OTHERWISE WE WOULD HAVE BEEN ISSUED A CLRNC SUCH AS 'YOU'RE CLRED VISUAL APCH RWY 34L; #3 TO FOLLOW A B737 AT YOUR 10-11 O'CLOCK POS AND X MI.' EVEN MORE CLR WOULD HAVE BEEN; 'YOU'RE CLRED VISUAL APCH RWY 34L; #3 TO FOLLOW A RED B737 ON A 6 MI FINAL.' THIS WOULD HAVE ALERTED US TO BE AWARE THAT THERE WERE ADDITIONAL ACFT AHEAD OF US; ESPECIALLY WHEN WE ARE SPEAKING OF SAME TYPES; IE; B737. POSSIBLY EVEN ANOTHER PROC WOULD HAVE BEEN TO GIVE VECTORS TO FINAL; ASSURING THAT WE WERE IN PROPER SEQUENCE; AND THEN CLR FOR THE VISUAL APCH. THIS SEEMS TO BE A CASE OF TOO MUCH TFC; AND TOO LITTLE INFO; NOT A CASE OF POORLY TRAINED OR COMPLACENT PERSONNEL FLYING BLINDLY. THIS CREW HAS PERSONALLY FLOWN INTO THE SLC AIRSPACE NUMEROUS TIMES A WK FOR THE PAST MANY YRS.