C402 MAKES GEAR UP LNDG. GEAR WARNING HORN DOES NOT ACTIVATE.

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ON VISUAL APCH TO RWY 36 AT ASG; STARTED TO EXTEND GEAR AND ELECTED TO HOLD IT; UNTIL CLOSER IN. TRIED TO CANCEL IFR WITH APCH; HOWEVER; UNSUCCESSFUL DUE TO RADIO CONGESTION. WENT BACK TO CTAF FOR POS ADVISORY; THEN BACK TO APCH TO REATTEMPT CANCELLATION; XMISSION WAS BLOCKED. BY THIS POINT I SELECTED SECOND NOTCH OF FLAPS. NO GEAR WARNING HORN WAS AUDIBLE. FAILED TO CHK GEAR DOWN 3 GREEN. SELECTED FULL FLAPS; PWR TO 15 INCHES MANIFOLD PRESSURE; NOR WAS THROTTLE GEAR WARNING HORN AUDIBLE. LANDED ACFT WITH GEAR IN RETRACTED POS. FACTORS CONTRIBUTING INCLUDE; 13TH HR OF DUTY; LAST OF 5 LEGS AND FATIGUE OF EARLY MORNING HR. DISTRACTIONS OF MODERATE TURB; RADIO CONGESTION. OTHER FACTORS INCLUDE MALFUNCTION OF GEAR WARNING SYS; AND IMPROPER USE OF CHKLIST. DAMAGE TO ACFT DID NOT REQUIRE RPT TO NTSB. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR STATES THAT MAINT INSPECTION INDICATED THAT GEAR WARNING HORNS WERE INOP ON BOTH MANIFOLD PRESSURE AND FLAP INDICATORS. HIS COMPANY IS SUPPORTING HIM AND OFFERED A FLT 2 DAYS LATER. HE HAS SUPPORT FROM THE FAA INSPECTOR WHO WAS ASSIGNED TO THE INCIDENT. INSPECTOR HAS SUGGESTED THAT THE RPTR USE THE INFORMAL HEARING PROC SINCE HE CAN THEN GIVE AN OPINION IN ADDITION TO THE FACTS HE STATED IN HIS FAA RPT. RPTR'S COMPANY HAS SCHEDULED CARGO AND PAX OPS.