CAPT OF LGT ACR ACFT INADVERTENTLY TAXIED PAST CLRNC LIMIT TO ACTIVE RWY RESULTING IN A NEW AMENDED CLRNC TO TAXI DOWN THE RWY. THIS HAPPENED AT NIGHT IN FOG AND RAIN.

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RECEIVED CLRNC TO TAXI TO RWY 3C VIA STANDARD TAXI AND REMAIN ON SAME FREQ. I RAN FIRST 2 ITEMS ON BEFORE TKOF CHKLIST STOPPING THE CHKLIST AS WE CROSSED RWY 9/27. ONCE ON THE OTHER SIDE WE RESUMED THE CHKLIST AND MOMENTARILY STOPPED ON TRIM SINCE WE HAD A DISCREPANCY IN THE TRIM INDICATORS. ONCE RESOLVED WE CONTINUED TO TAXI AND COMPLETE THE CHKLIST. AT THIS POINT WE WERE COMING UP ON A 45 DEG BEND IN THE TAXIWAY RTE TO THE END OF THE RWY WHERE TAXIWAY F INTERSECTS TAXIWAY X. AT THIS TIME THE LEAD FLT ATTENDANT OPENED THE COCKPIT DOOR TO MAKE HER REQUIRED RPT THAT THE CABIN WAS SECURED FOR TKOF. THE CAPT TURNED TO ACKNOWLEDGE HER AT WHICH TIME I LOOKED DOWN TO SWITCH MY MICROPHONE TO PA TO MAKE THE REQUIRED ANNOUNCEMENT THAT THE FLT ATTENDANTS BE SEATED FOR DEP. IT WAS DURING THIS EVENT THAT THE 45 DEG TURN WAS MISSED AND WE CONTINUED STRAIGHT AHEAD APCHING RWY 3C. THE CAPT ABRUPTLY APPLIED THE BRAKES AND WE STOPPED AT THE EDGE OF THE RWY. I BELIEVE THE CAUSE OF THIS MISSED TAXIWAY DUE TO THE INTERRUPTION BY THE FLT ATTENDANT DURING TAXI AND THE LACK OF ADEQUATE SIGNS. ALTHOUGH HER RPT IS REQUIRED; IT CAME AT THE WRONG TIME AND PROVIDED ENOUGH DISTR TO CAUSE A MISTAKE. CREW HAD BEEN ON DUTY 9 HRS AND 28 MINS AT TIME OF OCCURRENCE.