PLT OF C182 ON VOR APCH IN IMC HAS EQUIP IMPROPERLY SELECTED; WRONG SWITCH; AND IS 3 MI W OF COURSE WHEN ATC CALLS TO INFORM HIM.

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I WAS BEING VECTORED TO THE VOR A APCH TO Y47 ARPT. I SET THE APCH COURSE ON THE #2 VOR AND THE HSI/RNAV TO THE ARPT FOR THE PURPOSE OF DETERMINING THE VOR LOCATION AND THE MISSED APCH POINT; RESPECTIVELY. BOTH WERE SET TO THE PROPER FREQS AND COURSE SETTINGS. AT SOME POINT IN THE APCH AFTER PASSING THE VOR; I APPARENTLY FIXED MY ATTN ON THE HSI RATHER THAN THE VOR INDICATOR AND MADE SOME SIGNIFICANT CORRECTIONS TO CTR THE NEEDLE. I SIGHTED THE ARPT BUILDINGS (I THOUGHT) AND REDUCED ALT TO BE FULLY CLR OF THE CLOUDS. SOON AFTER I RECOGNIZED THAT I WAS NOT WHERE I THOUGHT I WAS; AND ABOUT THE SAME TIME ATC CALLED TO SAY THAT I WAS 3 MI W OF THE ARPT. I LOOKED TO THE R; AND SAW THE ARPT. I CANCELED MY CLRNC AND PROCEEDED TO THE ARPT ENTERING THE PATTERN TO RWY 7 ON A 45 DEG FROM THE N. I LANDED WITHOUT INCIDENT. THE PROB WAS CAUSED BY AN INCORRECTLY SET TOGGLE SWITCH WHICH CHANGES THE HSI INPUT FROM THE GPS TO THE RNAV. I HAD FLOWN TO THE PREVIOUS ARPT VFR AND HAD USED THE GPS. I RECOGNIZED THAT THE DATABASE WAS OUT OF DATE SO I FILED MY FLT AS A /R RATHER THAN A /G. I HAD NO REASON TO USE THE RNAV PRIOR TO THE APCH AS THE ENTIRE FLT WAS MADE BY VECTORS. THE HSI WAS GIVING INDICATIONS BASED ON THE INPUT FROM THE LAST GPS POS USED ON THE PREVIOUS FLT RATHER THAN THE LOCATION OF THE MISSED APCH POINT AS I INTENDED. WHEN I FIXED ON THE HSI RATHER THAN THE VOR; I WANDERED OFF COURSE. CORRECTIVE ACTION: SINCE I HAVE RECENTLY INSTALLED THE GPS; ALL OF MY TRAINING HAS BEEN TO FULLY UNDERSTAND THE CAPABILITIES OF ENRTE AND APCH FLYING USING THE GPS. I HAD NOT PRACTICED USING THE RNAV WITH THE NEW EQUIP INSTALLED. I FAILED TO TOGGLE THE HSI INDICATOR TO THE RNAV. I AM PLANNING TO TRAIN WITH BOTH THE GPS AND THE OTHER PRIMARY NAV EQUIP IN THE FUTURE. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR STATES THAT THIS WAS ENTIRELY A PROB OF NOT BEING FAMILIAR WITH THE SWITCHING ON THE EQUIP. HE FEELS THE GPS IS VERY PWRFUL BUT ALMOST DANGEROUS AS ONE GETS VERY LAZY USING IT AND IF THERE IS A FAILURE IT CAN CREATE MAJOR PROBS. RPTR IS CURRENTLY TRAINING WITH A CFI TO GET MORE FAMILIAR WITH PROPER PROCS.