As the title states. We have a '85 W123TD parts car with the tach/clock and a '78 W123 300CD with no tach. I don't understand the reasoning of having a tach in an automatic transmission car but it is not my car and not my place to question why.

What would be required to transfer the clock/tach into the 300CD instrument cluster and make it operable?

I'm sure a bit of wiring would need to be altered/added, the amplifier, gauge and the sending unit used from the 300TD but is there anything which would make this an absolute "no go"?

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