NON ADHERENCE TO ATC INSTRUCTION WHEN SMA PLT FAILS TO CHANGE FREQS TO ADVISORY FREQ AT PART-TIME ATCT ARPT ON IAP ILS APCH. NIGHT OP. TWR CLOSED.

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THE ATC TWR AT AZO WAS CLOSED AS I WAS CLRED FOR THE ILS 35 APCH AT AZO BY ZAU 20 MI OUT. AT THIS TIME; I WAS CLRED TO CHANGE TO THE ADVISORY FREQ (THIS IS THE CTAF OF 118.3 AT AZO). AT THE SAME TIME I WAS JUST GETTING ESTABLISHED ON THE LOC. AFTER I WAS ESTABLISHED; I COMPLETED THE FINAL APCH CHKLIST AND PROCEEDED DOWN THE ILS AND BROKE OUT JUST ABOVE MINIMUMS. I WAS SURPRISED TO SEE A COUNTY TRUCK ON THE RWY. IT WAS HIGHLY VISIBLE SINCE ITS HEADLIGHTS AND ITS FLASHING RED LIGHTS WERE BOTH ON. SINCE HE WAS FACING THE APCH END OF THE RWY; HE SAW ME IMMEDIATELY AFTER I BROKE OUT OF THE CLOUDS AND QUICKLY EXITED THE RWY. I LANDED SAFELY WITH NO OTHER INCIDENT. I HAD REALIZED THAT I HAD FORGOTTEN TO ANNOUNCE MY POS ON THE CTAF DUE TO MY EARLY HDOF AND REALIZATION THAT THE APCH WOULD BE CLOSE TO MINIMUMS. TO AVOID THIS SIT IN THE FUTURE; I HAVE ADDED 'ANNOUNCE POS ON CTAF' TO MY FINAL APCH CHKLIST. I HAD ALSO LEARNED TO NEVER ASSUME THERE IS NOBODY NEAR (OR ON) THE ARPT REGARDLESS OF THE WX OR THE TIME OF DAY. IN MY CASE; LOW IFR NEAR EARLY AM.