My 91 350 SDL also has a Klima (likely same set up as yours).
First noticed I had lost the Klima when both the AC and tachometer went out ... I took relay apart, cleaned it, carefully pried points apart (mine had three sets), reheated several of the solder joints and tried it. Worked for awhile, then went out again. Did the same thing again, but filed the points a bit. Back in and it worked again ... still working.
During the time when it didn't work, I was able to get it to work by schwacking it with a heavy wrench ... not elegant, but when it was 100F outside ... well ...
I found rebuilt ones with year guarantee at Beckmann Technologies (advertised in The Star) 800.742.1021, but have not yet ordered one as I am not finished playing with mine, yet.
Mine has a missing pin and connector, as well. I have been unable to find any other issues except the Klima that accounts for the problem.
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