A C172 PLT; TAXIING OFF RWY 27L AT OAK; EXITED THE TXWY IMPROPERLY AND BECAME STUCK IN THE SOD.

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I LANDED AFTER DARK ON OAKLAND'S RWY 27L WITH AN INOP TAXI AND LNDG LIGHT. TWR TOLD ME TO EXIT AT THE NEXT TXWY AND HOLD SHORT OF RWY 27R. I TURNED RIGHT BTWN 2 PARALLEL ROWS OF TXWY LIGHTS; WHICH I THOUGHT INDICATED THE EDGES OF A TXWY THAT I TURNED ONTO. I SOON DISCOVERED THAT I HAD ACTUALLY TURNED INTO A SOFT AND SOMEWHAT GRASSY AREA BTWN TXWYS H AND G; AND THE NOSEWHEEL GOT STUCK IN THE SOFT GND. THE ACFT WAS NOT DAMAGED. ATC CLOSED THE RWY. AFTER I WAS UNABLE TO PUSH BACK THE ACFT ONTO THE RWY BY MYSELF; THEY SENT OUT AN ARPT TRUCK. THE DRIVER WAS ABLE TO ASSIST ME IN PUSHING BACK ONTO THE PAVEMENT; AND I TAXIED TO PARKING. I SUBSEQUENTLY DISCUSSED THE MATTER BY TELEPHONE WITH A TWR PERSON; WHO SEEMED CONCERNED THAT THIS WAS MY SECOND FLT WITH AN INOP LNDG LIGHT ON THIS PARTICULAR ACFT. AFTER I POINTED OUT THAT OPERATING WITHOUT A LNDG LIGHT IS LEGAL IN OPS WHICH ARE NOT FOR HIRE; HE RECOMMENDED THAT SINCE I HAD TROUBLE TAXIING WITHOUT ONE; I SHOULD WAIT UNTIL DAYLIGHT BEFORE FLYING IT AGAIN. I TOLD HIM I WOULD CONSIDER IT; AND ENDED UP TAKING HIS RECOMMENDATION. MY PREVIOUS TRAINING IN TAXIING AT NIGHT WITHOUT A TAXI OR LNDG LIGHT HAD CONSISTED MAINLY OF WATCHING THE TXWY EDGE LIGHTS; WHICH WAS CLRLY NOT SUFFICIENT FOR THIS OP. THERE ARE SEVERAL ADDITIONAL MEASURES THAT COULD HAVE HELPED AVOID THIS EVENT: I COULD HAVE MADE MORE USE OF THE ARPT DIAGRAM. IT PROBABLY WOULD NOT HAVE BEEN APPROPRIATE TO STOP ON THE RWY TO CONSULT IT; BUT I SHOULD HAVE REVIEWED IT IN ADVANCE OF THE FLT; TAKING PARTICULAR NOTE OF THE CONFIGN OF THE TXWYS IN THE GENERAL VICINITY OF MY INTENDED PARKING AREA. I COULD HAVE DONE A BETTER JOB OF FAMILIARIZING MYSELF WITH THE CONVENTIONS FOR ARPT SIGNS. THE AIM STATES THAT TXWY DIRECTION SIGNS ARE NORMALLY LOCATED PRIOR TO THE INTXN. TAKING NOTE OF THIS COULD HAVE PREVENTED ME FROM TURNING TOO EARLY. I COULD HAVE CONTINUED STRAIGHT AHEAD ON THE RWY UNTIL I SAW THE TXWY LEAD-IN LINE; WHICH WOULD HAVE BEEN VISIBLE UNDER THE ILLUMINATION OF MY WINGTIP POS LIGHT. WHILE THE ABOVE MEASURES WOULD ALWAYS BE A GOOD IDEA; THEY WOULD HAVE BEEN ESPECIALLY ADVISABLE FOR A NIGHT FLT; AND DOUBLY SO WITHOUT A TAXI OR LNDG LIGHT. I ALSO THINK I ALLOWED THE FACT THAT I WAS ON AN ACTIVE RWY TO RUSH ME INTO TURNING BEFORE I WAS ABSOLUTELY SURE I WAS TURNING IN THE RIGHT PLACE. I SHOULD HAVE TAKEN MORE TIME.