NIGHT TRAINING FLT ENDS WITHOUT INCIDENT AFTER LOSING ALL ELECTRICAL SYS OVER AN UNDERCAST. HOWEVER; A TCA CLASS B AIRSPACE WAS ERRONEOUSLY ENTERED ON AN UNAUTH DSCNT THROUGH THE UNDERCAST LAYER.

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DUE TO SEIZED BEARINGS ALTERNATOR WAS SPLIT IN HALF. AS A RESULT WE EXPERIENCED ELECTRICAL FAILURE AT 7500 FT MSL. AT THAT TIME WE WERE ABOVE UNFORECASTED; MOSTLY OVCST LAYER OF CLOUDS NO RADAR COVERAGE WAS AVAILABLE DUE TO TERRAIN. DUE TO NO ARPTS WITHOUT PLT CTLED LIGHTING AND MOUNTAINOUS TERRAIN WE DECIDE TO CONTINUE AND HOPING THAT FORECAST WOULD BE RIGHT (VFR -- 25000 -- OVCST). WE TOOK A HDG AND TIME. WE WERE COUNTING BIG BLOBS OF LIGHTS AND TRYING TO IDENT THEM AS LARGE CITIES. WE ALSO CLBED TO 11500 FT TO GET BETTER LOOK AROUND. AFTER TIME FOR DSCNT CAME UP; WE STARTED QUICK DSCNT. WE ENTERED CLOUDS AT 8000 FT MSL AND BROKE OUT AT 6000 FT 5 MI AWAY FROM THE DEST. UNFORTUNATELY WE ALSO CLIPPED PART OF CLASS 'B' AIRSPACE ALTHOUGH WE WERE UNABLE TO ACTIVATE RWY LIGHTS. UNEVENTFUL LNDG WAS MADE ON UNLIGHTED RWY. DUE TO VERY EARLY HR ON A SUNDAY WE BELIEVE NO OTHER PLANES WERE WITHIN 20 MI OF US AT ANY TIME. IN CONCLUSION: TIME TO GET A HAND HELD RADIO AND MAYBE PORTABLE GPS. WE WERE LUCKY WEE HRS OF THE DAY REDUCED RISK OF COLLISION. KNOW ALL ARPTS WHERE RWY LIGHTS ARE ON ALL NIGHT!