PA28 BEING VECTORED FOR ILS TO SNA IS GIVEN WRONG DIRECTION TURN BY ATC TOWARD TERRAIN.

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ON MAR/THU/04 AT XA00; A TRAINING FLT WAS BEING CONDUCTED FROM MYF TO SNA UNDER AN IFR FLT PLAN. THE FLT WAS ORIGINALLY FILED FOR LGB THOUGH WE DECIDED TO GO TO SNA. THE FLT WAS BTWN VMC AND IMC DUE TO COASTAL FOG MOVING INTO THE BASIN WITH TOPS AROUND 4700 FT MSL. ABOUT 20 MI FROM OCN; ATC CLRED US TO 4000 FT MSL AND GAVE US A CLRNC TO EXPECT VECTORS FOR ILS RWY 19R SNA; SHORTLY AFTER WE GOT OUR FIRST VECTOR. OUR FLT WAS NOW OUT PAST THE OM AND WE WERE SE OF THE LOC. ATC GAVE US A VECTOR. IT WAS A R TURN TO A NW DIRECTION. I TOLD MY STUDENT TURN L AFTER HE WAS TURNING R. I THEN TOLD ATC 'THERE IS A MOUNTAIN OUT HERE (YOU MEAN L).' ATC REPLIED 'YES; TURN L.' AS WE WERE TURNING BACK; I COULD SEE THE PEAK OF THE MOUNTAIN. IF WE WOULD HAVE KEPT THE TURN COMING R; IT WOULD HAVE BEEN A CFIT ACCIDENT. ATC THEN CAME BACK AND SAID WE WERE LOW AT 3700 FT MSL. I LOOKED AT THE ALTIMETER AND THE ALT WAS 4000 FT MSL. THERE WAS PROBABLY A MODE C DISCREPANCY. AS WE WERE BEING VECTORED AGAIN; WE WERE CLRED R TO AROUND A S DIRECTION. I SAID 'YOU MEAN A L TURN.' ATC SAID 'YES; L; AND TRACK THE LOC INBOUND.' NOW OVER LEMON (OM) WE WERE ESTABLISHED. I CAME BACK AND SAID 'ARE WE CLRED FOR THE ILS RWY 19R APCH?' ATC SAID; 'CLRED FOR ILS RWY 19R APCH.' WE WERE THEN HANDED TO SNA TWR AND LANDED WITH NO FURTHER INCIDENT. WE WERE ALMOST PUT IN A MOUNTAIN. THOUGH; DUE TO SITUATIONAL AWARENESS; WE WERE ABLE TO TAKE CORRECTIVE ACTION. I FEEL THE CTLR WAS OVERWORKED AND AN ATC SUPVR SHOULD HAVE GIVEN HIM A BREAK OR TAKEN ACTION. THIS WAS A DANGEROUS SIT AND A SAFETY DANGER TO ALL ACFT ON THE NIGHT OF MAR/THU/04.