My 350SDL had an intermittent "tach not working" issue that recently became generally permanent ... shorter and shorter periods of working.
When it doesn't work, the air conditioner also is inop ... assume system is telling A/C that the engine is not running ...
Did yours follow this pattern? Did you fix yours? Any advice?
1991 350 SDL (200K and she ain't bent, yet)
former 2002 E320 4Matic Wagon - good car
former 1985 300 CD - great car
former 1981 300 TD - good car
former 1972 280 SEL - not so good car
a couple of those diesel Rabbits ...40-45 mpg