C172 ISTR AND STUDENT HAD TOTAL ELECTRICAL FAILURE AT NIGHT.

Narrative

I WAS DOING NIGHT FLT TRAINING WITH A STUDENT PLT ON FRI NIGHT OCT/FRI/01. WE WERE ABOUT 8 MI W OF DUPAGE ARPT WHEN WE LOST ALL ELECTRICAL EQUIP. THE DUPAGE ARPT BEACON WAS IN SIGHT AND AS PIC I DECIDED TO CONTINUE TO DUPAGE INSTEAD OF DIVERGING IN THE DARK. SEVERAL ATTEMPTS WERE MADE TO TROUBLESHOOT THE SYS WITHOUT SUCCESS. WE ALSO TRIED CALLING THE ARPT ON MY CELL PHONE BUT RECEIVED NO SIGNAL. WE THEN ENTERED THE VEIL OF CLASS B AIRSPACE AND INTO DUPAGES AIRSPACE WITHOUT RADIOS; LIGHTS OR A MODE C TRANSPONDER. WE CIRCLED OVER THE ARPT 500 FT ABOVE PATTERN ALT BUT THE CTLR DID NOT SEE US IN THE DARK. WE TRIED WAVING A SMALL FLASHLIGHT AROUND BUT THE CTLR STILL DID NOT SEE US. WE THEN RECEIVED A SIGNAL ON MY CELL PHONE AND WE CALLED THE DUPAGE FLT CENTER; THEY THEN RELAYED THE MSG TO THE TWR THAT WE NEEDED HELP. THE CTLR THEN GAVE US LIGHT GUN SIGNALS AND WE LANDED WITHOUT INCIDENT. IN THIS SIT; A DIVERSION TO AURORA COULD HAVE BEEN MADE SINCE NO MODE C IS REQUIRED THERE. HOWEVER; THE CTLR WOULD HAVE HAD THE SAME PROB NOT SEEING US IN THE DARK. DEKALB ARPT WAS NOT AN OPTION BECAUSE THE RWY LIGHTS WERE OFF AND WE HAD NO WAY TO TURN THEM ON. A FAULTY ALTERNATOR WIRE CAUSED THE PROB AND ALL BATTERY PWR WAS DRAINED. THE SIT CAN BE PREVENTED FROM HAPPENING AGAIN BY PAYING MORE ATTENTION TO THE AMMETER. AN EARLIER DETECTION OF A FAILURE WOULD HAVE ALLOWED US TO PRESERVE SOME PWR FOR THE RADIOS.