So I have my 1985 300D, CA emissions. The engine has been replaced with that from a 1983 300SD and the tranny has been replaced with that from a 1983 300D. No longer CA emissions. Tachometer does not work.

As I understand, the tach in this circumstance ran off of a computer, possibly getting signal from the transmission (?). The computer was in the passenger side kick area.

I'd like to cut the Gordian knot. The car has the conventional pickup from the front of the engine, leading to a diagnostic port on the left front wheel well. That is intact and connected. I have a tach amplifier for that port, and a wire extends from the diagnostic port to a mess of bundled wires on the way to the dash.

Can I do something to wire up the tach to function properly using the conventional set-up (not the set up that goes via the computer in the passenger wheel well?). What would I have to do to make my tach work?

__________________
Der Panzermann und Fraulein Fahrvergnuegen

1991 420SEL 201K "The Big Blue One"
1985 300DT 205K chassis/285K engine nee California emissions "Goldbug"
1983 300TDT 255K "The Womble"
1983 300 DT 214K "Sea Sprite"-Rear-ended a truck
1983 300SD 285K "The Donor" Gave his life so that others can live
1980 500SL Euro 105K "Der Panzer"