PARTIAL INST FAILURE IN IMC.

Narrative

THE ALTERNATOR BELT IDLER PULLEY FAILED; RESULTING IN LOSS OF ELECTRICAL PWR. THE FAILURE WAS INTERMITTENT FOR POSSIBLY 15-20 MINS WITH TOTAL ALTERNATOR FAILURE APPROX 45 MINS INTO FLT. THE PROB OCCURRED WHILE BEING VECTORED AFTER DEP FROM SLC ARPT. ALL READINGS WERE NORMAL WHILE BEING VECTORED INITIALLY SW OF SLC AND IN CLB UP TO 13000 FT. APPROX SE OF TOOELE; THE HSI AND BACKUP VOR WERE SHOWING DISCREPANCIES OF UP TO 20 DEGS. WHILE TRYING TO DETERMINE THE CAUSE OF NAV DISCREPANCIES; I PROBABLY BUSTED BOTH ALT AND AIRWAY LIMITS. I SUSPECTED VOLTAGE PROBS; BUT WHEN I GLANCED AT THE AMMETER; IT APPEARED TO BE NORMAL; DRAWING ABOUT 30 AMPERES. IT WASN'T UNTIL THE IDLER PULLEY FAILED COMPLETELY; TRIGGERING MY BATTERY WARNING INDICATOR; THAT I REALIZED I HAD AN ELECTRICAL PROB. AT THAT POINT IN TIME MY HSI AND VOR SHOWED SUBSTANTIAL DISCREPANCIES. I CALLED ATC AND REQUESTED VECTORS TO THE NEAREST ARPT WITH AN FBO. ALL UNNECESSARY ELECTRICAL DEVICES WERE SHUT OFF AND I ARRIVED AT CEDAR CITY AND LANDED WITHOUT INCIDENT. NO EMER WAS DECLARED. ON THE HUMAN FACTOR SIDE; 1 PLT IFR WAS VERY DIFFICULT IN HARD IMC WITH CONFLICTING INST READINGS.