A B737-300; OPERATED BY 2 TECHNICIANS; TAXIING THE ACFT ON AN INACTIVE RWY FOR TESTING INADVERTENTLY CROSSED THE HOLD SHORT LINE OF AN ACTIVE RWY.

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WHILE TAXIING; I CROSSED THE HOLD SHORT LINE OF THE ACTIVE RWY. ACR RETURNED TO THE GATE WITH 2 ABORTED TKOF ATTEMPTS DUE TO THE TKOF WARNING HORN SOUNDING. AT THE GATE FOLLOWING THE FAULT ISOLATION MANUAL/CHART; I COULD NOT DUPLICATE THE FAULT. I ALSO PERFORMED THE TKOF WARNING TEST PER THE MAINT MANUAL. THE TEST PASSED -- NO FAULTS. I ALSO INSPECTED THE TKOF WARNING SWITCHES (FLAPS; STABILIZER; SPD BRAKE) FOR CONDITION AND SECURITY. I DETERMINED THAT I WOULD TRY TO DUPLICATE THE CONDITIONS THE PLTS HAD. THIS WOULD MEAN RUNNING THE ENGS AT A HIGH PWR SETTING. WE REQUESTED FROM THE TWR A PLACE WHERE WE COULD PERFORM A PWR RUN AND WAS TOLD THAT WE COULD USE THE INACTIVE RWY (MY UNDERSTANDING). WE TAXIED TO THE RWY AND I ADVANCED THROTTLES PAST 33% (TO ACTIVATE THE TKOF WARNING SYS) WITH PARK BRAKE RELEASED. I TAXIED FOR A SHORT TIME TO SEE IF THE FAULT WOULD OCCUR WITH THE THROTTLES ADVANCED. NO WARNING HORN. I RETURNED THROTTLES TO IDLE AND STARTED BRAKING ACTION. I WAS NOT ABLE TO MAKE THE TXWY E TURNOFF AND DEPLOYED THRUST REVERSERS TO STOP AS QUICKLY AS I COULD. I WAS NOT AWARE THAT THE ACTIVE RWY WAS THE NEXT INTXN. WHEN THE ACFT WAS STOPPED IT WAS APPROX 1/2 AIRPLANE OVER THE HOLD SHORT LINE.