here, use this link. it will show you how to fix your tach. i had the same problem, and i did it. it works. http://schumanautomotive.com/forums/showthread.php?t=1842
as for the cruise control.. good luck. thats a whole other ball game

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1983 mercedes benz 300D turbo diesel.
pyrometer, boost/vacuum gauge
exhaust dump pipe
turbo- 15 psi boost. 25 psi capability
disconnected EGR