Taken from my green 521 thread. Another cluster problem just FYI.
I also put some leds in the dash lights. While I was in there I repaired a bad ground rivet that would make my left blinker light stay lit in the first pic. I would reach under there and tap the circuit board and the blinker light would go out for a while then come back on and stay lit when I tried to use the left blinker. I had this same rivet problem with my fuel gauge falling to empty again I would reach under the dash and tap the gauge volt reg and my fuel needle would jump up.
http://i272.photobucket.com/albums/jj172/dat521gatherer/datsun 521 1971 green/SANY8033_zpslfsx1swb.jpg
http://i272.photobucket.com/albums/jj172/dat521gatherer/datsun 521 1971 green/SANY8037_zps81eyh3t1.jpg
http://i272.photobucket.com/albums/jj172/dat521gatherer/datsun 521 1971 green/SANY8042_zpsy2letoko.jpg
http://i272.photobucket.com/albums/jj172/dat521gatherer/datsun 521 1971 green/SANY8045_zpscqv2dcvn.jpg