Check the ground wire at the light, and trace it back to where it grounds. Also, try swapping the bulb with the working one to make sure it isn't a bulb problem. My last guess would be to check the socket seat where the metal flange on th ebulb connects and make sure it is clean and has a good contact.
2003 Firemist Red/grey leather SL 500
2015 Palladium Silver/black mbtex GLK 350
1987 Smoke Silver/burgundy mbtex 300E Sportline (SOLD)
Click to see 87 300E