C172 PLTS HAVE ELECTRICAL FAILURE ENRTE TO THEIR DEST.

Narrative

WHILE CRUISING ENRTE FROM MCN TO GMU; WE EXPERIENCED ELECTRICAL FAILURE. WE WERE UNDER AN IFR FLT PLAN. THE FIRST THING WE NOTICED WAS A DISCHARGING AMMETER. AFTER TROUBLESHOOTING; WE WERE NOT CERTAIN IF THE ELECTRICAL SYS WAS DISCHARGING OR NOT. FOR INSTANCE; THE LOW VOLTAGE LIGHT WAS NOT ON. SHORTLY AFTER NOTING THE AMMETER (5 MINS) WE LOST INTERCOM AND HAD TO REMOVE HEADSETS. AT THIS POINT; WE BEGAN TO REALIZE THAT WE INDEED DID HAVE A DISCHARGING ELECTRICAL SYS. AT THIS POINT IT WOULD HAVE BEEN WISE TO DECLARE AN EMER. WE DID NOT; PERHAPS DUE TO CONFUSION AND CONTINUING TO TROUBLESHOOT. PERHAPS 2-3 MINS AFTER INTERCOM WAS LOST; WE LOST OUR ABILITY TO XMIT VOICE. COCKPIT AND INST LIGHTING ALSO WENT OUT. AT THIS POINT; WE IMMEDIATELY WENT TO BACK-UP FLASHLIGHTS AND BATTERY PWRED; HAND-HELD GPS. WE SET THE SQUAWK TO 7600; HIT THE 'IDENT' BUTTON; AND SHUT OFF REMAINING EQUIP. WE THEN USED THE GPS AND FLASHLIGHT AND MECHANICAL FLT INSTS TO FLY THE ACFT TO GMU. UPON 10 MI FROM GMU; WE TURNED ON #2 NAV/COM; AND COULD BARELY RECEIVE THE LOC SIGNAL. WE SHOT THE LOC WITH GPS BACK-UP TO LOC MINIMUMS (385 FT AGL). UPON REACHING MDA; I WAS ABLE TO SEE THE RWY. WE LANDED VISUALLY AND IMMEDIATELY CALLED THE FAA TO CONFIRM WE WERE ON THE GND; AND SAFE. IT TOOK BOTH MYSELF AND MY INSTRUCTOR; AT THE LIMIT OF OUR ABILITIES; TO SAFELY EXECUTE. I WILL NOT FLY IMC WITHOUT BACK-UP; BATTERY PWRED NAV/COM EQUIP EVER AGAIN.