STANDARD SEPARATION WAS LOST BETWEEN A C172 ON APCH AND ANOTHER ACFT; A SENECA.

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WHILE ACTING AS SAFETY PLT AND ASSISTING WITH COMS AND NAV; MYSELF AND THE OTHER PLT MAY HAVE MISSED INSTRUCTIONS FOR THE DIRECTION OF TURN TO A VECTORED HDG OF 250 DEG. AS INFORMED BY LCL FSDO: WE MADE A R TURN FROM OUR HDG OF 124 DEG WHICH TOOK US AWAY FROM THE OTHER ACFT I HAD IN SIGHT GOING APPROX FROM OUR 12 O'CLOCK TO 9 O'CLOCK POS. IT'S POSSIBLE I HAD THE WRONG ACFT IN SIGHT AND I COULD HAVE INFORMED ATC THAT IMC CONDITIONS EXISTED 300 FT BELOW OUR ALT AT THAT TIME. FROM WHAT I CAN RECALL; THERE WAS NO RESPONSE FROM ATC THAT A CONFLICT EXISTED BETWEEN US AND ANOTHER ACFT OTHER THAN CONFIRM TURNING 250 DEG. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR HAS BEEN CLRED OF RESPONSIBILITY IN SIT AND TOLD THAT THE CTLR WAS NOT ENTIRELY BLAMELESS. CTLR DID NOT RELAY THE URGENCY OF THE CLRNC. LTSS OCCURRED; THE TARGETS WERE LESS THAN 1 MI HORIZ AND AT THE SAME ALT. AFTER A L TURN TO INTERCEPT THE RADIAL; THE PLT RECEIVED A VECTOR TO 250 DEG AND RESPONDED WITHIN 10-15 SECONDS CORRECTLY; WITH A R TURN. RPTR WAS LATER TOLD THAT CTLR WAS AT A 'NEW POS' AND EXPERIENCING AN EXTREMELY HEAVY WORKLOAD. THE OTHER ACFT WAS AN IFR SENECA THAT HAD JUST BEEN HANDED OFF BUT WAS NOT IN RADIO CONTACT. CTLR WAS ATTEMPTING TO ESTABLISH COM WITH SENECA AND UNABLE. SUPPLEMENTAL INFO FROM ACN 315755: I WAS FLYING A CESSNA 172 ON AN IFR FLT PLAN FROM PAO TO APC; OPERATING THE CTLS FROM THE L SEAT. SAFETY PLT WAS LOOKING FOR TFC AND HANDLING THE TFC CALLS. CONDITIONS ABOVE THE LAYER OF STRATUS WERE EXCELLENT; WITH VISIBILITIES OF ABOUT 15 MI. OUR INITIAL CLRNC HAD BEEN TO THE SGD VORTAC; THEN TO APC DIRECT. OAK INSTRUCTED US TO FLY HDG 330 DEG UNTIL ABLE TO RECEIVE SGD; THEN DIRECT SGD. WE RESPONDED THAT WE WERE ALREADY DIRECT SGD; BUT DID NOT STATE OUR HDG. ATC INITIALLY OFFERED US THE VOR RWY 6 APCH AT APC; BUT WE INDICATED THAT WE WANTED THE LOC RWY 36L APCH. APCHING THE VOR ON A 305 DEG COURSE; WE WERE SLIGHTLY L OF COURSE AND ELECTED TO ROUND THE VOR VIA A R TURN. THE IAF IS ON THE SGD 124 RADIAL AT 3.8 DME; GIVING ADEQUATE ROOM TO JOIN THE 124 RADIAL. DURING THIS PHASE OF THE FLT; THE CTLR WAS COMMUNICATING EXTENSIVELY WITH ANOTHER ACFT. WE BELIEVE WE HAD EXECUTED A L TURN BACK TO JOIN THE RADIAL WHEN WE RECEIVED A 250 DEG VECTOR FROM ATC FOR TFC. AT THIS POINT; WE WERE AT OUR ASSIGNED ALT OF 3000 FT; 300 FT ABOVE A VERY SOLID STRATUS LAYER; BUT WITH GOOD VISIBILITY. WE DO NOT RECALL ANY SPECIFIC DIRECTION BEING GIVEN FOR THE TURN TO 250 DEG. THE COPLT SPOTTED THE TFC OFF TO OUR L AT AN ESTIMATED RANGE OF 1 MI; AND ABOUT 100 FT LOWER; COPLT RPTED SIGHTING TFC TO ATC; WHO ASKED US TO MAINTAIN VISUAL SEPARATION. ON COMPLETION OF THE TURN; THE TFC WAS RECEDING AND NOT A FACTOR. TFC WAS DIFFICULT TO SEE AT THIS POINT AS IT WAS BTWN THE L WING AND THE TAIL. ATC VECTORED US BACK TO THE LOC OUTBOUND. WE EXECUTED THE PUBLISHED PROC AND APCH UNEVENTFULLY. I RECEIVED A PHONE CALL FROM THE LCL FSDO; INFORMING ME THAT WE HAD TURNED IN THE WRONG DIRECTION TO 250 DEG ON THIS FLT. WE NOW REALIZE THAT WE MAY HAVE MISSED OR MISINTERPRETED AN INSTRUCTION TO TURN L TO 250 DEG FROM ATC. IT IS POSSIBLE THAT THE ACFT WE SAW WAS NOT THE ONE REFERRED TO BY ATC. WE HAVE LEARNED THAT BOTH PLT AND COPLT SHOULD XCHK RADIO COM AND THAT WE SHOULD INFORM ATC OF THE POS OF TFC AND OUR ABILITY TO MAINTAIN VISUAL SEPARATION IN SUCH A SIT.