What was found
RELAY CONTROLS THE APU CUT-OUT RELAY TO PREVENT USE OF WINDSHIELD HEAT WITHOUT THE GENERATOR OR APU ON-LINE. THIS RELAY SHORTED INTERNALLY WHICH POSSIBLY SENT A FALSE SIGNAL TO THE GCU WHICH CAUSED THE GENERATORS* TO GO OFF LINE IN-FLIGHT. AFTER EXTENSIVE TROUBLESHOOTING WITH CESSNA TECH SUPPORT, COULD NOT EXPLAIN WHY THIS HAPPENED IN-FLIGHT NOR COULD FIND ANY OTHER REPEATABLE CAUSE. ALL OTHER SYSTEMS OPERATE PROPERLY. *BOTH GENERATORS WENT OFF-LINE AND COULD NOT BE RESET.