SMA PLT FLYING AT NIGHT MISTAKES TAXIWAY FOR RWY. EXECUTES GAR.

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THE FINAL LEG (CRP-SAT) OF MY DAYTIME XCOUNTRY TRIP WAS DELAYED IN CRP SECONDARY TO MECHANICAL PROBLEMS WITH THE CARB HEAT CTL. AS MY FLYING EXPERIENCE IN OTHER THAN DAYLIGHT CONDITIONS WAS LIMITED; I ORIGINALLY PLANNED ON ARRIVING AT MY DEST ARPT (SAT) APPROX XA30 LCL TIME. HOWEVER; DUE TO THE TIME IT TOOK TO REPAIR THE CARB HEAT CTL IN CRP; I WAS UNABLE TO LEAVE CRP UNTIL XB40 LCL TIME. THE CRP-SAT LEG WAS UNEVENTFUL UNTIL ON FINAL APCH TO SAT. I WAS INSTRUCTED TO ENTER A R BASE FOR 12R AND GIVEN CLRNC TO LAND 12R BY SAT APCH THEN SAT TWR. I HAD THE FIELD IN SIGHT AND WAS ORIENTED DURING THE BASE LEG; HOWEVER WHEN I TURNED FINAL FOR 12R; I LOST SIGHT OF 12L AND ASSUMED THAT 12R (WHICH I WAS LINED UP ON) MUST BE 12L. BEING PARTIALLY DISORIENTED; I ALTERED MY FINAL LEG TO THE R; LOOKING FOR 12R. BY DOING THIS I WAS LINED UP WITH TAXIWAY G (WHICH IS PARALLEL TO AND TO THE R OF 12R). I MADE A HIGH APCH AND WAS AT APPROX 300 AGL FLYING OVER TAXIWAY G WHEN I SAW 2 PLANES ON THAT TAXIWAY; SAW THEM FLASH THEIR LNDG LIGHTS; REINTERPRETED THE BLUE TAXIWAY LIGHTS AND IMMEDIATELY MADE A GAR WITH THE TWR INSTRUCTING ME TO MAKE L TFC FOR 12L. I LANDED UNEVENTFULLY ON 12L. I WAS NOT IN IMMEDIATE DANGER OF COLLIDING WITH THOSE PLANES ON TAXIWAY G AS I HAD MADE A HIGHER FINAL APCH LEG TO GET A BETTER VIEW OF THE AREA. I REALIZE THAT I NEED TO BE MORE FULLY AWARE OF THE APPEARANCE OF THE ARPT ENVIRONMENT IN OTHER THAN DAYLIGHT CONDITIONS.