ACR MLG UNAUTH TAXI/UNAUTH RWY CROSSING.

Narrative

GIVEN TAXI INSTRUCTIONS ONTO INACTIVE RWY TO WAIT FOR CENTER RELEASE TIME. ACFT WAS ON TXWY O AT SWITCH FROM RAMP CTL TO GND CTL. PIT GND INSTRUCTED US TO TAXI VIA P TO RWY 32L; ON 32 HOLD SHORT OF G. NO PROB WITH TXWY P AND RWY 32 AS BOTH CAPT AND I HAD BEEN BASED AT THIS AERODROME FOR SEVERAL YRS. UPON TURNING LEFT (SE) ON RWY 32 I ASKED THE CAPT IF HE HAD ANY IDEA WHERE G WAS. HE REPLIED THAT HE HAD NO IDEA; BUT WOULD CONTINUE TAXIING ON RWY 32 UNTIL HE SAW A SIGN. I TOLD HIM THAT I'D HAVE A LOOK AT THE AIRFIELD DIAGRAM. HE REPLIED; 'DON'T BOTHER WITH THAT;' AND CONTINUED TAXIING. WHILE I WAS HEADS DOWN DIGGING OUT AND FIGURING OUT THE ARPT DIAGRAM; WE TAXIED PAST G; ACROSS RWY 28C (AN ACTIVE RWY) AND STOPPED SHORT OF C ON RWY 32. VIS WAS EXCELLENT AND CAPT COULD SEE THAT THERE WOULD BE NO CONFLICT XING RWY 28C; HOWEVER WE WERE NOT CLRED TO DO SO. GND INSTRUCTED US TO HOLD SHORT OF C ON RWY 32 TO AWAIT OUR RELEASE TIME AND THEN HAD US TAXI BACK FOR TKOF ON RWY 28C. HE INFORMED US OF OUR ERROR; WHICH I HAD MADE THE CAPT AWARE OF SHORTLY AFTER WE STOPPED AT C. FACTORS: CAPT CONTINUED TO TAXI; WHEN UNCLR OF ROUTE. COMPLETE LACK OF SIGNS OR OTHER GUIDANCE ON AERODROME. NO SIGN AT TXWY G OR C VISIBLE FROM RWY 32 TAXIING SEBND. F/O SHOULD HAVE HAD ARPT DIAGRAM PAGE OPEN AND AVAILABLE; BUT DID NOT DUE TO FAMILIARITY AND USUAL ROUTINE AT HOME DROME.