I just solved this problem in my 1982 300TD by replacing all of the fuses. I was completely mystefied, and someone on another forum mentioned that as the fuses age (approx 10 yrs old) the conductor crystalizes and causes problems. In my case, pushing the brake pedal caused all the gauges to die. One interesting thing was my Tachometer, horn and backup lights are on the same circuit, and those continued to work. I also had no turn signals or brake lights.

Happy Motoring

RBM