ACFT EQUIP PROB. APU FALSE WIRE WARNING. FLC DECLARED EMER AND DIVERTED FLT. B737-300.

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FLT FROM SJC TO ORD (MAY/XX/96). AT FL330 CRUISE; APPROX 1 1/2 HRS INTO THE FLT; WE WERE APCHING CHEYENNE; WY. WE HAD A MASTER CAUTION LIGHT AND FOUND IT TO BE THE 'APU DET INOP' LIGHT. WE REFERRED TO THE IRREGULAR PROC IN OUR FLT HANDBOOK. PARAPHRASING; IT BASICALLY SAID TO NOT USE THE APU; OR IF IT WAS ON; TURN IT OFF; AS WE DO NOT HAVE APU FIRE DETECTION. AS PER THE MAINT BOOK IN THE ACFT (MRM BOOK) I CALLED ACFT MAINT. THEY SAID SIMPLY TO 'WRITE THE PROB IN THE LOGBOOK -- WE'LL GET TO IT IN ORD.' THIS WAS ACCOMPLISHED. INCIDENTALLY; THE APU HAD BEEN SHUT OFF FOR APPROX 1 1/2 HRS -- SINCE PUSHBACK AT SAN JOSE. 15 MINS AFTER THE MASTER CAUTION; THE APU FIRE WARNING WAS TRIGGERED. THE CAPT IMMEDIATELY PERFORMED THE EMER PROC; PULLED THE FIRE HANDLE AND ROTATE. THE LIGHT IN THE FIRE HANDLE REMAINED ON SO WE DID AS INSTRUCTED -- LAND AT THE NEAREST SUITABLE ARPT. WE COULD HAVE LANDED AT CYS DIRECTLY BELOW; BUT BOTH OF US WERE UNFAMILIAR WITH THE FIELD. WAS THERE ADEQUATE EQUIP THERE FOR OUR SIT? WE DID NOT KNOW. ALSO; WE WERE AT FL330 SO THE DSCNT WOULD HAVE CONSUMED A LOT OF TIME (INTO CYS). THE CAPT HAD ALREADY TAKEN A DIRECT VECTOR TO DENVER AFTER DECLARING AN EMER. A FEW MINS AFTER THE EMER; WHEN THE SIT WAS UNDER CTL; I ADVOCATED MY FEELING/CHOICE OF LNDG AT THE 'NEAREST' SUITABLE ARPT (CYS). I THOUGHT DENVER WAS THE BETTER CHOICE; BUT I THOUGHT THE FAA WOULD CHOOSE CYS. THE CAPT DECIDED DENVER AS THE BEST CHOICE; AND IN HINDSIGHT; I AGREE. I WAS NOT DEAD SET ON CYS -- I JUST WANTED TO MAKE SURE WE WOULD CONSIDER IT AS AN ALTERNATIVE. CRM WAS DEFINITELY IN EFFECT ON THIS FLT AND MADE THE EMER SIT BE RESOLVED SAFELY; EFFECTIVELY; AND EFFICIENTLY.