MD80 FLC HAS RAMP EXCURSION WHEN TAXIING TO GATE.

Narrative

WE WERE TAXIING ONTO OUR RAMP AT NIGHT; AND THERE WAS SOME CONFUSION ABOUT WHETHER OUR GATE WAS OCCUPIED. WE TAXIED OVER TO THE EDGE OF THE RAMP TO STAY OUT OF THE WAY OF OTHER ACFT LEAVING THE RAMP; WHILE WE WORKED ON THE PROB OF THE GATE. THE PROB WITH THE GATE WAS THAT THE GATES HAD BEEN RENUMBERED AND THIS IS A NEW GATE. ONE ARPT CHART DOES NOT SHOW THIS GATE AND HAS THE OLD GATE NUMBERS. THE OTHER SHOWS THIS GATE WITH THE NEW NUMBERS. WE ACCIDENTLY WERE AT FIRST USING THE OLD CHART; WHEN WE CAME TO THE RAMP. ONCE ON THE RAMP WE REALIZED THE MISTAKE AND TAXIED OVER TO THE SIDE TO CLR THE RAMP AND CONSULT THE OTHER CHART. IN THE PROCESS OF DOING THIS THE R GEAR WENT OFF THE RAMP AND SANK IN THE MUD. THE PAX AND BAGGAGE WERE OFF LOADED THERE AND MAINT PERSONNEL DUG OUT THE R GEAR AND PUSHED THE ACFT BACK ON THE RAMP. NO ONE WAS HURT; AND AS FAR AS I KNOW; NO DAMAGE WAS DONE TO THE ACFT. CONTRIBUTING FACTORS: THE RAMP EDGE IS NOT LIT AND ON A DARK NIGHT THIS MIGHT HELP TO ALIGN YOURSELF WHEN TAXIING ON THE RAMP.