In the row of warning lights (battery, seat belt, brakes, etc) along the lower edge of the instrument cluster, there should be 2 little knobs about 1/4 inch diameter. The one on the right adjusts the clock. The one on the left is the instrument light rheostat. With the speedometer at rest, the speedo needle will be more or less pointing at the rheostat. Also, when you push that knob, it resets the trip odometer. (Don't push it when the car is in motion.) It's 99% guaranteed that your lighting problem is because the rheostat is dirty. Just keep rotating it back and forth until the lights want to stay on. You will find that you need to do this 2 or 3 times a year.
2004 C240 Wagon 203.261 Baby Benz
2008 ML320 CDI Highway Cruiser
2006 Toyota Prius, Saving the Planet @ 48 mpg
2000 F-150, Destroying the Planet @ 20 mpg
And remember folks, Only You Can Prevent Hilliary.