NON ADHERENCE TO ATC INSTRUCTION CREATES A RWY INCURSION. ACR MECH TAXIING MLG FOR SCHEDULED MAINT PROC GETS DISORIENTATED AND STOPS PAST RWY STOP LINE EVEN THOUGH HE HAD BEEN CLRED ACROSS.

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I WAS TAXIING AN MLG ACFT FOR A MAINT ENG TRIM RUN. I HAVE BEEN TAXIING THIS TYPE OF ACFT FOR 12 YRS. I WAS TAXIING FROM THE L SEAT AND IN THE R SEAT THERE WAS A MECH COMPLETELY UNFAMILIAR WITH TAXIING PROCS OR RADIO WORK. IT WAS NECESSARY TO CHANGE THE HDG THE TWR HAD GIVEN US DUE TO THE WIND. WE WERE TOLD TO MOVE TO A DIFFERENT LOCATION ON THE ARPT. THE TWR GAVE ME CLRNC TO CROSS RWY 31-13 THEN 12L-30R AT THE SAME TIME. AFTER I HAD CROSSED 31-13 THERE WAS SOME CONFUSION IN THE COCKPIT AND I STOPPED THE ACFT UNTIL I COULD GET CONFIRMATION FROM THE TWR. THE NOSE OF THE ACFT WAS OVER THE HOLD LINE FOR 12L-30R BUT NOT CLOSE TO THE RWY SIDE LINE. THE TWR THEN CALLED AND ASKED WHY WE STOPPED. WHEN I TOLD HIM I WASN'T SURE IF I HAD CLRNC HE SAID TO CROSS 12L-30R NOW. AS I DID A TWIN ENG COMMUTER ACFT DID A GAR. THE TWR THEN CALLED BACK AND SAID I HAD CAUSED THE GAR BECAUSE I HAD STOPPED OVER THE RWY HOLD LINE. WHEN WE WERE PARKED IN A DIFFERENT RUN UP AREA THE TWR CALLED BACK AND ASKED WHAT THE PROBLEM WAS. I EXPLAINED THAT I WAS RUNNING THE COCKPIT BY MYSELF AND THAT I HAD BECOME CONFUSED ABOUT THE CLRNC AND HAD STOPPED RATHER THAN CROSS AN ACTIVE RWY. I WASN'T SURE ABOUT HAVING CLRNC TO CROSS. I APOLOGIZED SEVERAL TIMES FOR THE MISUNDERSTANDING. THE TWR MADE NO MENTION OF IT AGAIN BUT I THOUGHT I SHOULD FILL THIS RPT OUT ANYWAY.