Don't matter diesel, does matter speed sensing.
If you have a Klima relay then you have engine speed sensing. If you have a tach then there is speed signal conversion, usually done by the EGR transducer on diesels (done by ignition controller on gas). I'm not sure how much electronics are on an 84 190D but if it has a klima it wants engine speed.
Bosch Master, ASE Master, L1
33 years MB technician