A PVT SMA PLT TAXIED OFF THE TXWY INTO THE MUD.

Narrative

WHILE TAXIING FROM THE ACFT'S TIE-DOWN POS AT FBO; I HEADED TO THE EDGE OF THE RAMP AS I USUALLY DO. THIS RAMP IS POORLY LIT AS IT FRINGES AND OTHER PARKED ACFT ARE OFTEN HARD TO SEE WHEN VISIBILITY IS LOW; SO I ALWAYS GO TO THE EDGE OF THE RAMP FOR SAFETY'S SAKE. MY FAMILY AND I HAD BOARDED THE ACFT IN THE RAIN AND THE INTERIOR OF THE ACFT WAS FOGGED. I WIPED THE FRONT AND SIDE WINDOWS OFF BUT VISIBILITY WAS LESS THAN PERFECT; SO I PROCEEDED SLOWLY. A STEADY RAIN WAS FALLING AND THERE ARE FEW MARKINGS ON THE RAMP AND NO LIGHTS MARK THE EDGE. I FOUND A YELLOW STRIPE THAT I MISTOOK FOR A CTRLINE MARKING FOR TAXIING ACFT. WHAT IT TURNED OUT TO BE WAS AN EDGE MARKING WHICH PUT ME TAXIING WITH THE R MAIN OF THE CHEROKEE 6 IN THE GRASS. WITHIN A FEW FT; THE TIRE FOUND A SOFT SPOT AND THE R MAIN SUNK INTO THE MUD. I NOTIFIED GND CTL; SECURED THE ACFT AND WALKED BACK TO THE FBO. THEY ACCOMPANIED ME BACK TO THE ACFT AND THE ACFT WAS PULLED BACK ONTO THE RAMP AND TAKEN TO THE HANGAR. WE REMOVED THE MUD FROM THE WHEEL WITH A WATER HOSE; INSPECTED THE WHEEL; AND RELOADED MY PAX. I CALLED TO PICK UP MY DELAYED CLRNC AND CONTINUED THE FLT. AT NO TIME WAS ANOTHER ACFT NEAR THE DISABLED CHEROKEE AND NO OTHER ACFT WERE MOVING ABOUT IN THIS AREA. THE ONLY DAMAGE WAS A SMALL RUT IN THE GRASS AT THE EDGE OF THE RAMP AND I AM NOT SURE IF THE RAMP IS CONSIDERED A PART OF THE RWY ENVIRONMENT. I THINK THAT MORE LIGHTING OR REFLECTORS ON THE EDGE OF THE RAMP WOULD CERTAINLY HAVE KEPT THIS FROM HAPPENING. IF CHEROKEE 6'S HAD BETTER/MORE LNDG/TAXI LIGHTS; I WOULD HAVE BEEN ABLE TO SEE THE GRASS AND WOULD HAVE MISSED THE MUD. I MAY HAVE BEEN A LITTLE TOO COMFORTABLE WITH MY FAMILIARITY OF THE RAMP AREA WHICH I WOULD NOT DO AT A STRANGE ARPT. I CAN THINK OF NO RULES THAT COULD KEEP THINGS LIKE THIS FROM HAPPENING. I WILL BE MUCH MORE CAREFUL IN THE FUTURE WHEN TAXIING AT NIGHT.