AN AC50 COMMANDER 500 LOSES ITS ALTERNATOR; RADIOS AND XPONDER ON AN IFR FLT TO PIR; SD. THE PLT MAINTAINS VMC AND FINDS PIR WITH HIS GPS AND THE FLOAT COMPASS.

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EXPERIENCING NOT AN IMMEDIATE INTERCEPT OF ASSIGNED VICTOR AIRWAY DEPARTING SUX; I ASKED FOR AND RECEIVED DIRECT MHE. THEN; ASCERTAINING THE MOA AHEAD WAS COLD; ASKED FOR AND RECEIVED DIRECT PIR. I WAS NOW NAVING BY GPS. ABOUT 45 MINS INTO THE FLT; I NOTICED A FLUCTUATION IN THE #1 HSI; AND CONFIRMED IT DID NOT MATCH INFO DISPLAYED BY THE GPS. AN ALTERNATOR RED LIGHT CAME ON INDICATING AN OFFLINE CONDITION AS I DETECTED A FAINT BURNING ODOR. CIRCUIT BREAKERS BEGAN TO POP AND THE AUTOPLT KICKED OFF. I WAS AT 8000 FT IN THE CLR ON TOP OF AN UNDERCAST; BUT APCHING HVY CLOUD COVER AT MY ALT. UNABLE TO CONTACT CTR; I ELECTED TO CLB TO 10000 FT TO REMAIN IN THE CLR TO TRY TO SORT OUT MY PROB. IN SCROLLING THROUGH; I INADVERTENTLY SET OFF BEACON 7500 THEN EVIDENTLY LOST THE XPONDER ALONG WITH BOTH NAV AND COM RADIOS PREVIOUSLY OUT. THE WX AT MY DEST WAS FORECAST SCATTERED FOR MY ARR TIME. ESTIMATING I WAS APPROX 30 MINS FROM PIR; I CONTINUED ON NAVING WITH THE GPS WHICH HAS A BACKUP BATTERY AND THE FLOAT COMPASS. 20 MI E OF PIR; I ENCOUNTERED THIN SCATTERED CLOUDS SO DSNDED TO 4500 FT; LNDG AT PIR IN CLR SKIES. INSPECTION BY MAINT AT PIR FOUND A FRAYED ALTERNATOR WIRE; BOTH BATTERIES COOKED. THE HSI AND BOTH NAV/COM RADIOS INOP. CAUSE: POSSIBLE ELECTRICAL SHORT. DAMAGE: ALTERNATOR (REPAIRED). BOTH BATTERIES REPLACED. HSI AND BOTH NAV/COM RADIOS TO BE REPAIRED. NOTE: ENTIRE NEW RADIO PACKAGE INSTALLED LESS THAN 3 MONTHS AGO. MAY OR MAY NOT BE RELEVANT.