A B727 CREW TAXIING FOR TKOF AT DTW; TAXIED THE NOSEWHEEL UP TO THE TXWY EDGE; REQUIRING THE AID OF A MARSHALLER.

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IT WAS A DARK AND MOONLESS NIGHT. WE WERE PUSHED BACK WITH OUR TAIL POINTED TO THE TXWY. GND CLRED US TO TAXI TO RWY 4R VIA 'TXWY K13 AND TXWY Y.' WE DID A 180 DEG TURN; WHICH PUT THE SIGN FOR TXWY K13 ON OUR R. IT SHOULD HAVE BEEN ON OUR L; BUT WE DIDN'T CATCH IT. THE LACK OF MOONLIGHT MEANT THE PAVEMENT WAS INDISTINGUISHABLE FROM THE GRASS BTWN TXWY K AND TXWY Y. OUR ACFT WAS ONE OF THE FEW IN THE FLEET WITH A TAXI LIGHT INSTALLED. HOWEVER; DUE TO ACFT XING IN FRONT OF US; I ELECTED NOT TO USE IT. GIVEN THE LIGHTING CONDITIONS; THIS WAS NOT A GOOD IDEA. JUST AS WE WERE ABOUT TO ENTER 'TXWY K13;' THE LAST ACFT PASSED IN FRONT OF US AND I FLIPPED ON THE TAXI LIGHT. WE WERE SHOCKED TO BE TREATED TO A SEA OF GREEN GRASS THAT EXTENDED ALL THE WAY UNDER THE NOSE OF THE ACFT. I IMMEDIATELY LOCKED THE BRAKES. WE WERE FORTUNATE THAT THE NOSE GEAR SITS QUITE A WAYS AFT. IT HAD NOT DEPARTED THE PAVED SURFACE. WITH THE HELP OF A MARSHALLER; WE MADE A 90 DEG TURN BACK TO THE PROPER DIRECTION ON THE TXWY. MY BIG LESSON LEARNED: SKIP THE COURTESIES AND USE THE LIGHTS WHEN YOU CAN'T SEE WHAT YOU'RE TAXIING ON.