GLF4 TAXIING TO PARKING AT ORD CROSSED RWY WITHOUT ATC CLRNC.

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DURING FLT FROM OMH TO CMH; OUR COMPANY CALLED AND ASKED THAT WE DIVERT TO ORD. AS WE WERE ONLY ABOUT 40 NM S OF ORD; THIS INVOLVED A HURRIED DSCNT AND ARR FROM FL410. WE HAD TO SET UP A SECOND APCH WHEN WE WERE GIVEN A DIFFERENT APCH THAN WE HAD BEEN TOLD TO EXPECT. AS I DID NOT HAVE TIME TO FULLY STUDY THE MAZE OF TXWYS AT ORD; I BRIEFED THAT WE WOULD FOLLOW OUR TAXI PROGRESS ON THE ARPT DIAGRAM AFTER LNDG; AND ASK FOR PROGRESSIVE IF NECESSARY FOR OUR TAXI TO FBO. AFTER LNDG ON RWY 27L WE WERE CLRED TO TAXI ON TXWY B TO HOLD SHORT OF RWY 32R. THIS WAS MODIFIED TO FOLLOW AN ACFT DOWN TXWY B. WHEN THE ACFT CONTINUED ONTO TXWY D TOWARD THE OLD FBO LOCATION; WE BECAME CONFUSED CONCERNING OUR CLRNC AND THE NEW LOCATION OF FBO. THE PIC ASKED FOR PROGRESSIVE. THE COMS WHICH FOLLOWED WERE SLOPPY ON BOTH ENDS. DESCRIPTIONS OF THE RTE TO FBO WERE MIXED WITH CLRNCS; BOTH OF WHICH WERE STEPPED ON BY OTHER ACFT. BY THE TIME WE REACHED RWY 32R WE WERE CONFUSED AS TO WHAT THE LIMIT OF OUR CLRNC WAS AND I STOPPED SHORT. THE PIC SAID THAT THE NEXT INTERSECTING RWY; WHICH TURNED OUT TO BE RWY 27R; WAS THE PLACE WE WERE TO HOLD SHORT AND WE WERE CLRED ACROSS RWY 32R. SOMETHING CLICKED IN MY HEAD THAT HE WAS RIGHT AND I DID HEAR A HOLD SHORT CLRNC FOR A RWY BEYOND RWY 32R. I CONTINUED ACROSS RWY 32R AFTER TAKING A LONG LOOK BOTH L AND R (ANOTHER PART OF MY MIND WAS SCREAMING CAUTION; BUT NOT QUITE LOUD ENOUGH) UNTIL OUR PROGRESS WAS BLOCKED BY A STATIONARY ACFT WHICH HAD SEEMED FARTHER AWAY IN THE DARKNESS. AT THIS TIME THE TWR TOLD US WE HAD JUST CROSSED THE ACTIVE DEP RWY. AFTER FOLLOWING THE CTLR'S INSTRUCTIONS TO UNBLOCK THE OTHER ACFT; I FINALLY STOPPED THE ACFT; ASKED FOR THE ARPT DIAGRAM; AND BRIEFED THE POSSIBLE RTES TO THE NOW IN SIGHT FBO. AFTER A SHORT WAIT; GND CLRED US TO THE RAMP AND WE CONTINUED WITHOUT FURTHER INCIDENT. AFTER SHUTDOWN; THE PIC CONTACTED THE TWR CAB AND DISCUSSED THE SIT TO EVERYONE'S SATISFACTION. WHILE THE MESS THAT IS ORD; AND SOME CONFUSING COMS FROM GND CTLRS PLAYED A PART IN THIS TRANSGRESSION; IT WOULD NEVER HAVE HAPPENED IF WE HAD ADMITTED OUR CONFUSION; STOPPED THE ACFT ON A VACANT TXWY; AND PLANNED OUR COURSE OF ACTION. FURTHER; WE SHOULD HAVE ASKED FOR A HOLD ON OUR HURRIED DSCNT INTO ORD AND MORE THOROUGHLY BRIEFED OUR TAXI IN. ORD IS NO PLACE TO OPERATE OFF YR OLD MEMORIES OF ARPT LAYOUT.