What was found
LEFT FWD WINDOW HEAT OVERHEAT ILLUMINATED IN FLIGHT, 27 MINUTES AFTER TAKEOFF, IN CRUISE FLIGHT, AT FL360. RAN QRH, NO HELP, OVERHEAT LIGHT ILLUMINATED. SELECTED LEFT FWD WINDOW HEAT OFF IAW QRH. SAT -60C. ACFT GROUNDED. BITE CHECK OF LEFT FWD WHCU FAULTS WINDOW SENSOR FOUR TIMES IN FAULT HISTORY. SECONDARY SENSOR IS OPEN, MEASURED AT WINDOW TERMINALS. PRIMARY AND SECONDARY WIRING CONTINUITY OK BETWEEN WINDOW AND WHCU. REINSTALLED LEFT FWD WHCU AND SECURED. REQUIRES REPLACEMENT WINDOW IAW FIM 30-41 TASK 812. NEW WINDOW RESISTANCE CHECKED AND TAP MOVED TO APPROPRIATE TERMINAL IAW WDM 30-41-11. REPLACED L1 WINDOW IAW AMM 56-11-11. LEAK AND OPS CHECKED GOOD.