AN ACR TURBOJET TURNED OPPOSITE TO ITS VECTOR DIRECTION FOR TFC AVOIDANCE. TRACK HDG ERROR; ERROR ADMITTED. EVASIVE ACTION WRONG WAY TURN.

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DURING DSCNT FROM 12000 FT; ATC ADVISED TFC AT 12 O'CLOCK WITH TYPE/ALT UNKNOWN. TFC WAS OBSERVED ON TCASII; DISPLAYED ON THE FMC TRACK LINE; AND CLOSING. A SCATTERED CLOUD LAYER BELOW OUR ALT WAS PRESENT; AND IT APPEARED THAT OUR DSCNT WOULD TAKE US INTO OR THROUGH THE CLOUDS. AS TFC WAS NOT VISUAL; NOR WAS ITS ALT DISPLAYED ON TCASII; I REQUESTED AN AVOIDANCE VECTOR. ATC DIRECTED A 20 DEG R TURN. BY THE TIME THAT THE VECTOR WAS RECEIVED; IT APPEARED THAT ONLY A L TURN WOULD ASSURE LATERAL SEPARATION. THE CAPT INITIATED A L TURN AND I ADVISED ATC. AFTER A SHORT TIME; WE CLRED THE TCASII TFC AND RESUMED OUR ORIGINAL HEADING. THIS IS A DIFFICULT PROB TO REMEDY. A MIX OF VFR/IFR TFC IN THE DENVER AREA; BUSY ATC FREQS; AND WX CONSTRAINTS TO VISUALLY ACQUIRING TFC WILL CAUSE MANY REOCCURRENCES. ATC APPARENTLY DOES NOT ISSUE AVOIDANCE VECTORS FOR NON MODE C VFR TFC UNLESS PLT REQUESTED; AND THERE IS A TENDENCY TO DELAY REQUESTING AVOIDANCE VECTORS AS ONE SEARCHES FOR THE TFC. WHEN WE DECIDED TO ASK FOR A VECTOR; WE WERE UNABLE TO BREAK IN ON A BUSY FREQ. WHEN WE FINALLY RECEIVED CLRNC; IT BECAME APPARENT THAT THE ATC ASSIGNED HEADING WOULD NOT ASSURE LATERAL CLRNC.